PC §9.51 ARREST AND SEARCH
(b) A person other than a peace officer (or one acting at his direction) is justified in using force against another when and to the degree the actor reasonably believes the force is necessary to make or assist in making a lawful arrest, or to prevent or assist in preventing escape after lawful arrest if, before using force, the actor manifests his purpose to and the reason for the arrest or reasonably believes his purpose and the reason are already known by or cannot reasonably be made known to the person to be arrested.
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