Motion to Strike: When Rule 12(f) Is Actually Worth Filing

A motion to strike asks the court to delete part of a pleading. Under Federal Rule of Civil Procedure 12(f), the court may strike "an insufficient defense or any redundant, immaterial, impertinent, or scandalous matter." Federal courts view these motions with disfavor and grant them infrequently. File one only in a narrow set of situations — most are wasted fees.

This article is general information, not legal advice. For a specific case, consult a licensed attorney in your jurisdiction.

What Rule 12(f) actually reaches

A court may act "on its own," or "on motion made by a party either before responding to the pleading or, if a response is not allowed, within 21 days after being served with the pleading."

The five categories are terms of art, read narrowly. Most pages just repeat them; here is what each means:

Those quoted definitions come from Fantasy, Inc. v. Fogerty, 984 F.2d 1524, 1527 (9th Cir. 1993), reaffirmed in Whittlestone, Inc. v. Handi-Craft Co., 618 F.3d 970, 974 (9th Cir. 2010); "scandalous" traces to Wright & Miller § 1382.

Note what is not on the list: weak, exaggerated, annoying, or badly written. Rule 12(f) is not a style guide.

The timing rule and its traps

• Attacking a complaint: file before you serve your responsive pleading. Once your answer is docketed, the window has closed.
• Attacking an answer or its affirmative defenses: 21 days after service. No response to an answer is allowed unless the court orders a reply under Rule 7(a)(7), so the 21-day clock governs.
• The court's own motion: unlimited. Rule 12(f)(1) lets a judge strike sua sponte at any point.

A motion to strike is also a motion "under this rule," so Rule 12(g)(2)'s consolidation requirement applies. You do not get to file a motion to dismiss now and a motion to strike later.

Why courts deny most of them

The line in the brief filed against you:

Rule 12(f) motions are generally viewed with disfavor "because striking a portion of a pleading is a drastic remedy and because it is often sought by the movant simply as a dilatory tactic."

Waste Management Holdings, Inc. v. Gilmore, 252 F.3d 316, 347 (4th Cir. 2001). The Eighth Circuit agrees: striking pleadings is an extreme measure, and these motions are infrequently granted. Stanbury Law Firm, P.A. v. IRS, 221 F.3d 1059 (8th Cir. 2000).

Three things follow.

Prejudice is an element, not decoration. Most courts will not strike unless the matter bears no possible relation to the controversy and leaving it in would prejudice you. Irrelevance alone loses; credited prejudice is concrete, like an allegation that drags a new subject into discovery.

Surplusage does not hurt you. No jury reads the complaint. If your honest answer to "what changes if I win?" is "the pleading is tidier," you have your answer.

The motion signals something. One aimed at a rhetorical flourish spends credibility you will want later. Same discipline as a motion in limine package: file what changes the case, skip the rest.

The four situations where it is worth filing

1. Scandalous allegations that will travel. A complaint is a public document. If it accuses your client of conduct with no bearing on any claim — an affair, an unrelated arrest, a slur — and a jury pool or a reporter will read it, move to strike. This is the one category where reputational harm is the prejudice.

2. An affirmative defense with no legal basis that would expand discovery. If a defense is legally unavailable and letting it stand means depositions on a subject that does not belong in the case, the prejudice is visible. Check your circuit's standard first: the Ninth Circuit held in Kohler v. Flava Enterprises, Inc., 779 F.3d 1016, 1019 (9th Cir. 2015) that fair notice requires only describing a defense in "general terms." No circuit has adopted Twombly/Iqbal for affirmative defenses, and district courts remain split.

3. Immaterial matter that meaningfully broadens discovery. Same logic, aimed at the complaint. An allegation about a decade of unrelated corporate conduct is not noise — it becomes the plaintiff's justification for a document request.

4. Class allegations that could never be certified. In the Ninth Circuit the vehicle is Rule 23(d)(1)(D), which lets a court require "that the pleadings be amended to eliminate allegations about representation of absent persons."

Notice what is missing: striking a damages claim as unavailable as a matter of law. That is the most common misuse of the rule, and in the Ninth Circuit it is foreclosed — Whittlestone held that Rule 12(f) "does not authorize a district court to strike a claim for damages on the ground that such damages are precluded as a matter of law." That is a Rule 12(b)(6) or summary judgment argument; relabeling it does not lower your burden.

What Rule 12(f) cannot touch

Anything that is not a pleading. Rule 7(a) defines the universe: complaints, answers (including to counterclaims and crossclaims), third-party complaints and their answers, and a court-ordered reply. Briefs, declarations, and exhibits are not on it. The Ninth Circuit put it plainly in Sidney-Vinstein v. A.H. Robins Co., 697 F.2d 880, 885 (9th Cir. 1983): only pleadings are subject to motions to strike.

Summary-judgment evidence. Settled by rule, and still gotten wrong weekly. Rule 56(c)(2) lets a party object that cited material "cannot be presented in a form that would be admissible in evidence," and the 2010 Advisory Committee Note says the quiet part out loud: "There is no need to make a separate motion to strike."

In both, ask the court to disregard rather than strike — one sentence in a brief instead of a motion, a hearing, and a denial.

Motion to strike versus motion in limine

The distinction: pleadings versus evidence.

The word "strike" does double duty: judges also strike trial testimony with an instruction to disregard, a third thing entirely, made orally, mid-trial. If your target is something a jury might hear, you want a motion in limine.

The more successful cousin: striking an improper filing

The use that actually works is not a Rule 12(f) motion at all. When an opponent files a sur-reply without leave, blows a page limit, files late, or attaches material a court order excluded, courts strike it — under their inherent authority over their dockets and local rules that say so. These succeed far more often, because the question is not "is this immaterial?" but "did this filing violate a rule?" Cite the rule or standing order violated, and move promptly instead of saving the point for your next brief.

State practice diverges, and California's is a different animal

California has two devices. The ordinary motion to strike, Code of Civil Procedure § 436, is broader than the federal rule: a court may strike "any irrelevant, false, or improper matter inserted in any pleading," and any pleading not drawn or filed in conformity with state law, a court rule, or a court order. Section 435.5 requires meeting and conferring first.

The special motion to strike — anti-SLAPP, § 425.16 — is not pleading cleanup at all. It is a dispositive motion aimed at claims arising from protected petitioning or speech:

• The claim is stricken unless the plaintiff "has established that there is a probability that the plaintiff will prevail." § 425.16(b)(1).
• It may be filed within 60 days of service of the complaint, or later in the court's discretion. § 425.16(f).
• All discovery is stayed on filing. § 425.16(g).
• A prevailing defendant "shall be entitled to recover that defendant's attorney's fees and costs." § 425.16(c)(1).
• An order granting or denying it is immediately appealable. § 425.16(i).

Many states have anti-SLAPP statutes, and they differ in scope, deadline, and fee-shifting. Never reason about one from Rule 12(f): the discovery stay, mandatory fees, and interlocutory appeal make it a different decision.

Before you file, price the motion honestly

The question is not "can I make this argument?" It is "what does the case look like if I win, and what did the brief cost?" For most Rule 12(f) motions the honest answers are "identical" and "four billable hours."

When one clears that bar, the research is jurisdiction-first: your circuit on striking defenses, your district's rule on non-pleading filings, your judge's standing order. That is where finding controlling authority in your own court beats finding a good case anywhere. CaseRead searches your firm's case files and the public law in one query, scoped to the matter you are on, and every citation traces to a source it actually retrieved.

And if any part of the brief came out of a general-purpose AI tool, check it first. Our Hallucination Shield is free, no signup: paste the draft, and each citation it finds — up to 50 per run — is checked for existence and support.

Frequently asked questions

What is a motion to strike? A motion to strike asks the court to remove specific material from a pleading. Under Federal Rule of Civil Procedure 12(f), a court may strike an insufficient defense or any redundant, immaterial, impertinent, or scandalous matter. It is a scalpel, not a dispositive motion: granting it deletes words and the case continues. An attack on a whole claim is a Rule 12(b)(6) motion.

When is a motion to strike due in federal court? Rule 12(f)(2) lets a party move either before responding to the pleading or, if no response is allowed, within 21 days after being served with it. So a motion aimed at a complaint must come before the answer, and one aimed at an answer must come within 21 days. The court may also strike on its own at any time.

Are motions to strike ever granted? Yes, but courts call them disfavored and infrequently granted. The Fourth Circuit explained in Waste Management Holdings, Inc. v. Gilmore that striking part of a pleading is a drastic remedy often sought as a dilatory tactic. Most courts require both no possible relation to the controversy and prejudice to the movant.

Can you file a motion to strike an affidavit or a brief? Not under Rule 12(f). The rule reaches only pleadings as Rule 7(a) defines them: complaints, answers, third-party complaints, and a court-ordered reply. Briefs, declarations, and exhibits are not pleadings, and the Ninth Circuit held in Sidney-Vinstein v. A.H. Robins Co. that only pleadings are subject to motions to strike.

What is the difference between a motion to strike and a motion to dismiss? A motion to dismiss under Rule 12(b) attacks a claim or the case; granted, it ends something. A motion to strike attacks words inside a pleading; granted, it deletes them and the case proceeds. The Ninth Circuit held in Whittlestone, Inc. v. Handi-Craft Co. that Rule 12(f) cannot strike a damages claim as precluded by law.

How long do you have to respond to a motion to strike? The Federal Rules set no single opposition deadline; local rules do, and they commonly give 14 to 21 days. Rule 6(c)(1) requires that a written motion and notice of hearing be served at least 14 days before the hearing, and Rule 6(c)(2) requires opposing affidavits at least 7 days before. Check the local rule.