If you join a pickup basketball game, you accept that someone may bump into you. That is the idea behind assumption of the risk: a person who voluntarily takes part in an activity with inherent risks assumes those risks.

As a legal defense to negligence: a coparticipant in a sport generally owes no duty to avoid the ordinary carelessness that is part of the game. Liability arises only for intentional injury or for conduct entirely outside the range of ordinary activity in the sport (CACI No. 470, citing Knight v. Jewett).

Against strict liability: assumption of the risk can be raised even when the claim is based on strict liability. In Priebe v. Nelson (2006), summarized in CACI No. 463, a kennel worker assumed the risk of being bitten by dogs in her care by the nature of her occupation, so her claim under the dog bite statute (Civil Code §3342) was unavailable.

Bottom line: strict liability removes the need to prove negligence, but it does not eliminate every defense. Assumption of the risk is one that survives.