Cross-claims trip up a surprising number of bar takers — not because the rule is complicated, but because it looks deceptively simple until you’re staring at a fact pattern with three defendants and a contribution dispute.

Let’s fix that.

What Is a Cross-Claim Under Rule 13?

A cross-claim is a claim asserted by one party against a co-party — meaning a party on the same side of the litigation. Most commonly, you’ll see this as one defendant asserting a claim against another defendant. But cross-claims can also run from one plaintiff to another plaintiff, though that scenario rarely shows up on the MBE.

The governing rule is Federal Rule of Civil Procedure 13(g). Under Rule 13(g), a party may assert a cross-claim against a co-party if the claim arises out of the same transaction or occurrence that is the subject matter of the original action, or if the claim relates to any property that is the subject matter of the original action.

Two things to notice immediately. First, cross-claims are permissive, not compulsory. You are never required to bring a cross-claim. Miss it, and you can still bring that claim in a later lawsuit. This is the exact opposite of compulsory counterclaims under Rule 13(a), which are lost if not asserted. That distinction is a favorite MBE test point.

Second, the same-transaction-or-occurrence requirement is a real limitation. Not every dispute between co-defendants qualifies. The claim has to be factually connected to what the original lawsuit is about.

The Elements the MBE Actually Tests

When you see a cross-claims question on the MBE, the examiners are usually probing one or more of these specific issues:

1. Co-party status. The cross-claim must be against a co-party — someone already in the lawsuit on the same side. You cannot use Rule 13(g) to bring in a brand-new third party. If a defendant wants to drag in someone not yet in the lawsuit, that’s a third-party claim under Rule 14, not a cross-claim.

2. Same transaction or occurrence. The cross-claim must arise from the same transaction or occurrence as the original claim, or must relate to property that is the subject of the original action. Think of it this way: if the cross-claim would require a completely separate trial with completely different facts, it probably doesn’t qualify.

3. Permissive nature. As noted above, cross-claims are never compulsory. A party who fails to bring a cross-claim does not waive it. This is tested directly — expect a question that asks whether a defendant who didn’t file a cross-claim is barred from suing later. The answer is no.

4. Contingent claims are allowed. A cross-claim can be contingent. A defendant can assert a cross-claim saying, in effect, “If I’m found liable to the plaintiff, then my co-defendant is liable to me for contribution or indemnification.” You don’t have to wait for the original claim to be resolved before asserting the cross-claim.

A Hypothetical to Make This Concrete

Here’s a fact pattern in the style of an MBE question:

A truck driver and a road construction company are both named as defendants in a personal injury lawsuit filed by a pedestrian. The pedestrian alleges that both defendants were negligent and caused her injuries. The truck driver believes the construction company is primarily responsible and wants to seek indemnification from the construction company. Can the truck driver assert a cross-claim against the construction company?

Yes. The truck driver and the construction company are co-parties — both defendants in the same lawsuit. The indemnification claim arises directly out of the same accident that forms the basis of the pedestrian’s original complaint. Same transaction, same occurrence. Rule 13(g) is satisfied. The cross-claim is permissive, so the truck driver may assert it, but is not required to.

Now change the facts slightly. Suppose the truck driver also wants to assert a claim against the construction company for a completely unrelated contract dispute — a separate delivery contract that went sideways three years ago. That claim does not arise from the same transaction or occurrence as the pedestrian’s personal injury suit. It does not relate to the same property. Rule 13(g) does not permit that cross-claim. The truck driver would need to file that as a separate lawsuit.

Cross-Claims vs. Counterclaims: Don’t Confuse Them

This is where students lose points. The MBE will test whether you can correctly classify the claim.

A counterclaim under Rule 13(a) or 13(b) is a claim against an opposing party — typically a defendant asserting a claim back against the plaintiff. A cross-claim under Rule 13(g) is a claim against a co-party — same side of the lawsuit.

Compulsory counterclaims must be raised or they’re waived. Cross-claims are always permissive. And third-party claims under Rule 14 bring in entirely new parties. These three are distinct. Know which one applies based on the relationship of the parties, not just the direction of the claim.

Jurisdiction Over Cross-Claims

Here’s a nuance that shows up less often but is absolutely fair game: once a valid cross-claim is asserted under Rule 13(g), does the court have jurisdiction over it?

Because cross-claims by definition arise from the same transaction or occurrence as the original action, they almost always qualify for supplemental jurisdiction under 28 U.S.C. § 1367. The same common nucleus of operative fact that ties the cross-claim to the original action is exactly what supplemental jurisdiction requires. So you generally don’t need an independent basis for federal jurisdiction over a cross-claim.

This is a meaningful contrast to certain other joinder devices. Under § 1367(b), supplemental jurisdiction is restricted in diversity cases for claims by plaintiffs against persons joined under Rules 14, 19, 20, or 24. Cross-claims under Rule 13(g) are not on that restricted list. Defendants asserting cross-claims against co-defendants in a diversity case can typically rely on supplemental jurisdiction without issue.

What Happens After a Cross-Claim Is Filed?

Once a cross-claim is asserted, the co-party against whom it is directed must respond. They have the same response options as any party responding to a claim — they can answer, assert defenses, and even assert their own cross-claims or counterclaims arising from the same facts.

The cross-claim becomes part of the same lawsuit and is resolved in the same proceeding, which is the whole point. Rather than litigating the same accident in three separate lawsuits, Rule 13(g) allows the court to resolve all related claims between all parties at once.

The FlashTables Reference

FlashTables is a set of professionally formatted two-column PDF rule tables covering all seven MBE subjects — 704 rules total, organized by the official NCBE Subject Matter Outline. The cross-claim rule under Rule 13(g), including its permissive nature and same-transaction requirement, is laid out side-by-side with related joinder rules in the Civil Procedure table. Whether you’re a 1L, 2L, or 3L building your civil procedure outline, or a bar taker drilling active recall in the final weeks before the MBE, the tables give you the black-letter rule in a format you can actually use under time pressure. You can see what’s covered at getflashtables.com.

Key Takeaways: Cross-Claims Under Rule 13 for the MBE

Before you move on, lock in these points:

The MBE isn’t trying to trick you on cross-claims. It’s testing whether you actually know the rule and can apply it cleanly when the fact pattern mixes defendants, contribution disputes, and joinder issues all at once. Know the elements cold, and you’ll spot the right answer fast.