OPINION
POLLAK, District Judge:
Robert Hunter and Howard Eley, the plaintiffs in this § 1983 action, sought to prove at trial that they were subjected to excessive force while in custody at the Sacramento County Main Jail pursuant to the County’s allegedly unconstitutional custom or practice of using excessive force at the Main Jail. The jury found in favor of the County, and the District Court denied plaintiffs’ motion for a new trial. In this appeal, plaintiffs argue that the District Court erred by refusing to use certain jury instructions they requested. Because we agree that the District Court erred, and that its error was prejudicial, we reverse the District Court’s order and remand for a new trial.
I
Plaintiffs initiated this action on March 3, 2006, and filed their Second Amended Complaint (“Complaint”) on August 22, 2006. The Complaint alleges that, on September 17, 2005, plaintiff Hunter was arrested for driving while under the influence. He was taken to the Sacramento County Main Jail (“Main Jail”), where he was placed in a detox cell with a clogged and overflowing toilet. The Complaint further alleges that when Hunter alerted several deputies of the Sacramento County Sheriffs Department about the toilet’s condition, the deputies responded by throwing him to the floor and applying force that resulted in a fractured elbow, stretched tendons, and nerve damage. The Complaint also alleges that plaintiff Eley was an inmate at the Main Jail, and that on March 21, 2004, Eley had a verbal disagreement with a deputy sheriff, after which the sheriff shoved, slapped, and choked Eley without provocation.
Plaintiffs’ Complaint named a number of defendants and asserted several causes of action. In its September 8, 2008 ruling on the defendants’ summary judgment motion, the District Court dismissed all of plaintiffs’ claims except for their Monell
claim against the County of Sacramento (“defendant” or “County”). Plaintiffs’
Monell
claim alleged that they were subjected to excessive force, in violation of their rights under 42 U.S.C. § 1983, pursuant to defendant’s longstanding practice or custom of subjecting inmates at the Main Jail to excessive force.
In its ruling denying summary judgment on this claim, the District Court’s opinion placed primary emphasis upon a declaration submitted by plaintiffs’ expert, Lieutenant Twomey, a former employee of the Sacramento County Sheriffs Department (“Sheriffs Department”). Lt. Twomey declared that there were 40 to 50 “major incidents” of excessive force at the Main Jail from 2000 to 2005. Lt. Twomey also declared that officials in the jail repeatedly failed to investigate the incidents, discipline the guards, or take other action to address the problem. For example, no Internal Affairs investigation was opened after a detainee named Jafar Afshar filed a complaint alleging that he had been subject to excessive force in the Main Jail
when a deputy grabbed him from behind and threw him backward, smashing his head onto the floor. A Sheriffs Department official later admitted that an investigation should have been opened but was not. Similarly, Lt. Twomey declared that, in his experience, an internal investigation should have been opened when inmate Mihaita Constantin suffered a fractured nose and hand after being thrown to the ground and having his wrists restrained by five deputies, none of whom were injured in the altercation. The Court found that all of this evidence created a material issue of fact as to whether the County had a practice or custom of using excessive force, despite the fact that the County had formal written policies prohibiting the use of excessive force.
On September 25, 2008, about a month and a half before trial, the District Court instructed the parties to submit proposed jury instructions. On October 14, plaintiffs and defendant both submitted proposed jury instructions. Plaintiffs offered 21 proposed instructions, 12 of which elucidated various ways in which a plaintiff may establish municipal liability under
Monell.
On October 31, the District Court issued its own set of proposed jury instructions, instructing the parties to submit any suggested modifications as soon as possible.
The instruction of central relevance to this appeal laid out the elements of a
Monell
claim for the use of excessive force in violation of the Fourth Amendment
(“Monell
instruction”). The District Court’s proposed
Monell
instruction read, in its entirety, as follows:
Each Plaintiff alleges that the Defendant County of Sacramento violated his Fourth Amendment constitutional right against use of excessive force. To prevail on this claim each Plaintiff must prove by a preponderance of the evidence each of the following elements:
First, that one or more of Defendant’s employees used excessive force against Plaintiff in violation of the Fourth Amendment of the United States constitution.
Second, that in so doing, Defendant’s employee or employees acted pursuant to a longstanding practice or custom of Defendant.
Third, that Plaintiff was injured; and, Fourth, that Defendant’s longstanding practice or custom was so closely related to Plaintiffs injury that it was the moving force causing Plaintiffs injury.
Excerpts of Record (“ER”) at 14. Both parties filed objections and proposed modifications to the District Court’s instructions. The document filed by plaintiffs began as follows: “PLEASE TAKE NOTICE that Plaintiffs object to the proposed Jury Instructions proffered by the Court, and request the following modifications.” In the body of the document, plaintiffs explained that they did “not object to [the
Monell
instruction] as written,” but they “specifically requested] the following proposed instructions be provided as well, as they state the law in the Ninth Circuit accurately, and in this District.” Plaintiffs then listed the following ten additional instructions, all of which were taken from their earlier list of proposed instructions and addressed standards for liability under
Monell.
(1) The routine failure to follow a general policy can itself constitute an actionable custom.
(2) Plaintiff can establish municipal liability against Defendant by proving that the excessive force was committed pursuant to a longstanding practice or custom which constitutes the “standard operating procedure” of the local governmental entity.
(3) Regardless of whether the County has formal policies regarding the use of
force, routine failure to follow a general policy can itself constitute an actionable custom.
(4) Failure to properly investigate, like failure to discipline employees involved in incidents of excessive force, is evidence of and supports a finding that not only was it accepted, but was customary.
(5) Plaintiff may also attempt to prove the existence of a custom or informal policy with evidence of repeated constitutional violations for which the errant municipal officials were not discharged or reprimanded.
(6) Policy or custom may be inferred if, after the use of excessive force, the County of Sacramento took no steps to reprimand or discharge the deputy sheriffs, or if they otherwise failed to admit the deputy sheriffs’ conduct was in error.
(7) The County is liable for depriving Plaintiff of a federal right if it is determined it did an affirmative act, participated in another’s affirmative acts, or omitted to perform an act which it was legally required to do that causes the deprivation.
(9) Liability for an established custom can be imposed irrespective of whether official policy makers had actual knowledge of the practice at issue.
(11) Failure to properly investigate, like failure to discipline employees involved in incidents of excessive force, is evidence of and supports a finding excessive force was not only accepted but was customary.
(12) The extent and openness of excessive force supports an inference that managerial level employees should have known.
ER 35-37 (citations omitted).
Each of these instructions was accompanied by a citation to one or more cases providing legal support for the stated proposition.
The District Court thereafter issued a final set of jury instructions for use during trial. ER 8-11 (excerpting relevant instructions). The Court did not adopt any of plaintiffs’ proposed supplemental instructions. Appellants’ Br. at 6. Indeed, the District Court’s order did not acknowledge that plaintiffs had filed supplemental instructions, or explain why it was not using any of those instructions. ER 8.
The final instructions did reflect the County’s suggestion that the definition of the term “practice or custom” used in Ninth Circuit Model Civil Jury Instruction 9.4 (2007) be added to the proposed
Monell
instruction. That definition specifies that “ ‘[pjractice or custom’ means any permanent, widespread, well-settled practice or custom that constitutes a standard operating procedure of the defendant.” Ninth Circuit Model Civil Jury Instruction 9.4 (2007) (“Model Instruction 9.4”). The court incorporated this definition in a separate instruction in its final set of jury instructions.
Trial began on August 4, 2008, and the District Court instructed the jury on August 12, 2008. The jury was given general verdict forms which asked whether each plaintiff had “prevailed] on his Fourth Amendment claim against the County of Sacramento” and, if so, what amount of damages was caused by the County. The jury returned a verdict in favor of the County and against both of the plaintiffs.
Plaintiffs filed a motion for a new trial on November 24, 2008, which argued, in
relevant part, that the District Court had failed to instruct the jury on the law as proffered in plaintiffs’ proposed additional jury instructions. The District Court rejected plaintiffs’ retrial request on January 8, 2009, finding that it was “based on a one sentence conclusory argument which assumes Plaintiffs’ proposed instructions were not considered before the jury instructions were finalized.” ER 3. The court also concluded that plaintiffs did not show “that the instructions given failed to ‘fairly and adequately cover the issues’ tried.” ER 4 (quoting
Duran v. City of Maywood,
221 F.3d 1127, 1130 (9th Cir.2000)). Plaintiffs filed a timely notice of appeal on February 9, 2009.
II
Plaintiffs object to the jury instructions used by the District Court on several grounds. Defendant argues that the instructions given were appropriate and that plaintiffs have waived their arguments concerning the instructions. We conclude that plaintiffs properly objected to the District Court’s refusal to use plaintiffs’ supplemental
Monell
instructions, and that the District Court erred by declining to use those instructions.
A.
We begin by addressing whether plaintiffs properly objected to the District Court’s
Monell
instruction. Under Federal Rule of Civil Procedure 51, “[a] party who objects to an instruction or the failure to give an instruction must do so on the record, stating distinctly the matter objected to and the grounds for the objection.” Fed.R.Civ.P. 51(c)(1). An objection to a jury instruction “ ‘need not be formal,’ ” and a party may properly object by submitting a proposed instruction that is supported by relevant authority, so long as the “proffered language [is] ‘sufficiently specific to bring into focus the precise nature of the alleged error.’ ”
Norwood v. Vance,
591 F.3d 1062, 1066 (9th Cir.2010) (quoting
Inv. Serv. Co. v. Allied Equities Corp.,
519 F.2d 508, 510 (9th Cir.1975)). If a party does not properly object to jury instructions before the district court, we may only consider “a plain error in the instructions that ... affects substantial rights.” Fed.R.Civ.P. 51(d)(2).
Plaintiffs have indeed made certain arguments for the first time in this appeal — arguments that we find unpersuasive.
However, the plaintiffs did properly object to the District Court’s proposed
Monell
instruction, to the extent that it did not go farther and failed to include a separate definition of practice or custom. In their objections to the District Court’s instructions, plaintiffs stated that they did “not object to [the Court’s proposed
Monell
instruction] as written,” but they asked that the Court also use the ten instructions quoted in Part I of this opinion, which elaborate various ways in which a
Monell
plaintiff may prove a practice or custom. We find that the ground for plaintiffs’ objection was made clear in their proposed instructions, which plaintiffs correctly, if inartfully, argued “state the law in the Ninth Circuit accurately, and in this District.”
Id.
Under Rule 51, objections to jury instructions must “stat[e] distinctly the matter objected to and the grounds for the objection.” Fed.R.Civ.P. 51(c)(1). As the Supreme Court has noted, “objections to a charge must be sufficiently specific to bring into focus the precise nature of the alleged error.”
Palmer v. Hoffman,
318 U.S. 109, 119, 63 S.Ct. 477, 87 L.Ed. 645 (1943). In applying Rule 51(c) in
Voohries-Larson,
we noted that a party objecting to a jury instruction may “put the court on notice by offering alternative instructions that were denied.” 241 F.3d at 715 (citing
Gulliford v. Pierce Cnty.,
136 F.3d 1345, 1348-49 (9th Cir.1998)). Likewise, in our decision last year in
Norwood,
we held that a party sufficiently objected by proposing alternative instructions that “made the grounds for their position clear, citing relevant authority.” 591 F.3d at 1066. In this case, the plaintiffs proposed their own jury instructions that defined
and explained the practice or custom prong and referred to several of our leading cases. By submitting instructions that specifically focused on the practice or custom prong of the
Monell
test, the plaintiffs put the District Court on notice of the grounds for their objection.
It should be noted that the County’s submission of the definition of practice or custom contained in Model Instruction 9.4 did not cure plaintiffs’ objection. As will be discussed in the following section, the County’s definition failed to make clear to the jury that the plaintiffs could prove that an unofficial practice or custom of excessive force existed at the Main Jail by pointing to inaction in the face of repeated instances of the use of excessive force by Main Jail employees. By contrast, the plaintiffs submitted instructions which explicitly stated that an unconstitutional practice or custom could be proven through evidence that incidents of excessive force were not investigated and their perpetrators were not disciplined.
See, e.g.,
ER 37 (Instruction No. 11: “Failure to properly investigate, like failure to discipline employees involved in incidents of excessive force, is evidence of and supports a finding excessive force was not only accepted but was customary.” (citations omitted)). These very specific proposed instructions were sufficient to put the District Court on notice that the plaintiffs considered the County’s proposed definition of custom or practice, taken from Model Instruction 9.4, to be incomplete and misleading. Thus, plaintiffs’ pre-trial objection to the District Court’s proposed
Monell
instruction was sufficient under Rule 51.
B.
We now turn to the merits of plaintiffs’ objection to the District Court’s “custom or practice” instruction. Our jury instruction decisions have traditionally distinguished between errors in the “formulation” of a jury instruction, which we review for abuse of discretion, and a jury instruction’s “misstate[ment ofj the law,” which we review de novo.
Dream Games of Ariz., Inc. v. PC Onsite,
561 F.3d 983, 988 (9th Cir.2009) (internal quotation omitted);
see also Dang v. Cross,
422 F.3d 800, 804 (9th Cir.2005). As our decision in
Nor-wood
recognized, we engage in de novo review when a party challenges a “jury instruction as an incomplete, and therefore incorrect, statement of the law.” 591 F.3d at 1066 (citing
Clem v. Lomeli,
566 F.3d 1177, 1180-81 (9th Cir.2009);
Dang,
422 F.3d at 804-06).
We have repeatedly held that “ ‘[j]ury instructions must fairly and adequately cover the issues presented, must correctly state the law, and must not be misleading.’ ”
Dang,
422 F.3d at 804 (quoting
White v. Ford Motor Co.,
312 F.3d 998, 1012 (9th Cir.2002)). We have also recognized that a district court’s “‘[u]se of a model jury instruction does not preclude a finding of error.’ ”
Id.
at 805 (quoting
United States v. Warren,
984 F.2d 325, 328 (9th Cir.1993)). Rather, each party is “ ‘entitled to an instruction about his or her theory of the case if it is supported by law and has foundation in the evidence.’ ”
Clem,
566 F.3d at 1181 (quoting
Dang,
422 F.3d at 804-05). However, if the “error in the jury instruction is harmless, it does not warrant reversal.”
Dang,
422 F.3d at 805 (citing
Tritchler v. Cnty. of Lake,
358 F.3d 1150, 1154 (9th Cir.2004)).
In
Monell,
the Supreme Court held that municipalities may be held liable as “persons” under 42 U.S.C. § 1983, but cautioned that a municipality may not be held liable for the unconstitutional acts of its employees solely on a respondeat superior theory. 436 U.S. at 691, 98 S.Ct. 2018. Rather, the Supreme Court has “required a plaintiff seeking to impose liability on a municipality under § 1983 to identify a
municipal ‘policy’ or ‘custom’ that caused the plaintiffs injury.”
Bd. of Cnty. Comm’rs v. Brown,
520 U.S. 397, 403, 117 S.Ct. 1382, 137 L.Ed.2d 626 (1997) (citing
Monell,
436 U.S. at 694, 98 S.Ct. 2018;
Pembaur v. Cincinnati,
475 U.S. 469, 480-81, 106 S.Ct. 1292, 89 L.Ed.2d 452 (1986);
City of Canton v. Harris,
489 U.S. 378, 389, 109 S.Ct. 1197, 103 L.Ed.2d 412 (1989)). In justifying the imposition of liability for a municipal custom, the Supreme Court has noted that “an act performed pursuant to a ‘custom’ that has not been formally approved by an appropriate decisionmaker may fairly subject a municipality to liability on the theory that the relevant practice is so widespread as to have the force of law.”
Id.
at 404, 117 S.Ct. 1382 (citing
Monell,
436 U.S. at 690-91, 98 S.Ct. 2018).
As noted above, the District Court’s initial
Monell
instruction required each plaintiff to prove that (1) “one or more of Defendant’s employees used excessive force against Plaintiff in violation of the Fourth Amendment”; (2) “that in so doing, Defendant’s employee or employees acted pursuant to a long-standing practice or custom of Defendant”; (3) “that Plaintiff was injured”; and (4) “that Defendant’s longstanding practice or custom was so closely related to Plaintiffs injury that it was the moving force causing Plaintiffs injury.” ER 14.
However, the District Court’s initial proposed instruction did not include a definition of the term “practice or custom.” Both parties objected to this omission, with the plaintiffs submitting the ten instructions quoted in Part I of this opinion, and the County submitting the definition of practice or custom used in Model Instruction 9.4.
The District Court’s final set of jury instructions adopted the definition taken from Model Instruction 9.4, which defines practice or custom as follows: “ ‘Practice or custom’ means any permanent, widespread, well-settled practice or custom that constitutes a standard operating procedure of the defendant.” ER 11. The series of qualifiers in this definition — “permanent,” “widespread,” “well-settled,” and “standard operating procedure” — emphasize that a practice must be pervasive and of significant duration.
This definition is certainly consistent with our
Monell
decisions, which have recognized that “[l]iability for improper custom may not be predicated on isolated or sporadic incidents” and that “[t]he custom must be so ‘persistent and widespread’ that it constitutes a ‘permanent and well settled city policy.’ ”
Trevino v. Gates,
99 F.3d 911, 918 (9th Cir.1996) (quoting
Monell,
436 U.S. at 691, 98 S.Ct. 2018);
see also Villegas v. Gilroy Garlic Festival Ass’n,
541 F.3d 950, 964 (9th Cir.2008) (holding that municipal liability may be established “by showing ‘a longstanding practice or custom which constitutes the standard operating procedure of the local government entity’ ” (quoting
Ulrich v. City & Cnty. of San Francisco,
308 F.3d 968, 984-85 (9th Cir.2002)));
Webb v. Sloan,
330 F.3d 1158, 1164 (9th Cir.2003);
Henry v. Cnty. of Shasta,
132 F.3d 512, 523 (9th Cir.1997).
While the definition of practice or custom in Model Instruction 9.4 is consistent with our
Monell
decisions, it is far from a complete statement of our caselaw. We have long recognized that a custom or practice can be “inferred from widespread practices or ‘evidence of repeated constitutional violations for which the errant municipal officers were not discharged or reprimanded.’”
Nadell v. Las Vegas Metro.
Police Dep’t,
268 F.3d 924, 929 (9th Cir.2001) (quoting
Gillette v. Delmore,
979 F.2d 1342, 1349 (9th Cir.1992),
abrogated on other grounds as recognized in Beck v. City of Upland,
527 F.3d 853, 862 n. 8 (9th Cir.2008));
see also Menotti v. City of Seattle,
409 F.3d 1113, 1147 (9th Cir.2005);
McRorie v. Shimoda,
795 F.2d 780, 784 (9th Cir.1986).
The plaintiffs submitted an instruction using language taken directly from our decision in
Gillette. See
ER 36 (Instruction No. 5: “Plaintiff may also attempt to prove the existence of a custom or informal policy with
evidence of repeated constitutional violations for which the errant municipal officials were not discharged or
reprimanded.” (citing
Gillette,
979 F.2d at 1349;
McRorie,
795 F.2d at 784) (emphasis added)). The plaintiffs also submitted a similar instruction that an unconstitutional custom could be inferred from the failure to investigate repeated instances of unconstitutional conduct.
See
ER 37 (Instruction No. 11: “Failure to properly investigate, like failure to discipline employees involved in incidents of excessive force, is evidence of and supports a finding excessive force was not only accepted but was customary.” (citations omitted)). However, the District Court, without explanation, declined to use either of these instructions.
Plaintiffs had good reason to submit these instructions, because the theory they explain was key to their case. Their expert, Lt. Twomey, found that officials in the Main Jail repeatedly failed to investigate incidents of excessive force and to take disciplinary action against guards who used such force, despite the existence of an official policy prohibiting the use of excessive force.
These instructions were vital to plaintiffs’ case, because the legal principle in plaintiffs’ instructions — that
evidence of a recurring failure to investigate and discipline municipal officers for constitutional violations can help establish the existence of an unconstitutional practice or custom — cannot be readily deduced from simply reading the definition of practice or custom in Model Instruction 9.4.
See
Model Instruction 9.4 (“ ‘Practice or custom’ means any permanent, widespread, well-settled practice or custom that constitutes a standard operating procedure of the defendant.”);
see also Norwood,
591 F.3d at 1067 (observing that “juries are not clairvoyant” and will not know to follow a particular legal principle “unless they are told to do so”). Accordingly, in the context of this case the definition of practice or custom in Model Instruction 9.4 was “an incomplete, and therefore incorrect, statement of the law.”
Norwood,
591 F.3d at 1066;
see also Fikes v. Cleghorn,
47 F.3d 1011, 1013 (9th Cir.1995) (holding that jury “instructions must allow the jury to determine the issues presented intelligently”). Further, by stating that a practice or custom must “constitute[ ] a standard operating procedure of the defendant,” Model Instruction 9.4 may well have encouraged the jury to disregard evidence that the County failed to investigate and punish the use of excessive force. We do not commonly speak of a failure to act as a “standard operating procedure.”
See Dang,
422 F.3d at 804 (noting that we have “stressed that jury instructions ... must not be misleading” (internal quotation and alteration omitted)). For these reasons, the District Court’s decision not to use the plaintiffs proposed instructions was in error.
We also conclude that this error cannot be considered harmless. “We presume prejudice where civil trial error is concerned and the burden shifts to the defendant to demonstrate that it is more probable than not that the jury would have reached the same verdict had it been properly instructed.”
Dang,
422 F.3d at 811 (internal quotations and alterations omitted).
Plaintiffs hoped to establish a “practice or custom” sufficient to create
Monell
liability despite the fact that the County had submitted evidence that the Main Jail had a formal written policy barring the use of excessive force that was nominally in place at the time of the events in question in this case. ER 20. If credited, Lt. Twomey’s testimony would have established that there were repeated constitutional violations at the Main Jail “for which the errant municipal officials were not discharged or reprimanded,”
Gillette,
979 F.2d at 1349, and that, in turn, could have supported an inference that an informal but widespread custom of using excessive force existed at the Jail. On the record before us, we find that such evidence might well have swayed the jury to reach a different result.
Without the plaintiffs’ proposed instructions, however, the jury would not have known whether to consider the evidence that numerous instances of excessive force at the Main Jail were never investigated
and that their perpetrators were not punished. Indeed, as discussed above, there is some risk that the jury, relying solely upon the definition of practice or custom in Model Instruction 9.4, would have thought it improper to consider such evidence at all. Consequently, we cannot conclude that it is more probable than not that the instructional error was harmless.
Ill
We hold that the District Court prejudicially erred in refusing to instruct the jury that, for purposes of proving a
Monell
claim, a custom or practice can be supported by evidence of repeated constitutional violations which went uninvestigated and for which the errant municipal officers went unpunished. We therefore vacate the judgment and remand for a new trial.
VACATED AND REMANDED.