Moving Force Causation

What It Is

Moving force causation is the causation requirement for municipal liability under Monell. It is not enough to show that a city had a bad policy and that you suffered a constitutional violation. You must prove the policy directly caused your injury — that it was the “moving force” behind the violation.

The Supreme Court established this standard in Monell v. Department of Social Services, 436 U.S. 658 (1978) and reinforced it in Board of County Commissioners v. Brown, 520 U.S. 397 (1997).

What You Must Show

Moving force causation has two parts:

1. But-for causation — The violation would not have occurred without the city’s policy, custom, or failure to train.

2. Proximate causation — The connection between the policy and the violation must be close and direct, not remote or attenuated. Board of County Commissioners v. Brown.

Examples

Strong causation:

• A city has an explicit policy allowing officers to use chokeholds during routine arrests. An officer applies a chokehold and injures you. The policy was the moving force.
• A department has zero training on how to interact with people experiencing mental health crises. An untrained officer uses deadly force against a person in crisis. The training failure was the moving force.

Weak causation:

• A city has a generally lax disciplinary culture, but the officer who harmed you acted in a way completely unrelated to any policy gap. The connection is too attenuated.
• A city negligently hired an officer who later committed a random, unforeseeable act. In Board of County Commissioners v. Brown, the Court found this insufficient without a more direct link.

Why It Matters

Moving force causation is where many Monell claims fail. Plaintiffs can often identify a bad policy, but struggle to prove it caused their specific injury rather than being a background condition.

Practical Tips

• Draw a direct line from the policy to your injury. Explain step by step how the policy led to the officer’s specific conduct that harmed you.
• Use the policy’s own language. If the policy authorized or encouraged the exact type of conduct that violated your rights, quote it.
• Show the training gap matches the harm. For failure-to-train claims, show that the missing training directly relates to the type of violation you experienced.
• Expert witnesses can help establish that proper policies or training would have prevented the incident.
• Gather evidence of similar incidents. A pattern of the same type of violation under the same policy strengthens the causal connection.

Key Takeaway

Identifying a bad policy is not enough — you must prove that policy was the driving force behind your specific constitutional injury. Draw a clear, direct line from policy to harm.