A defendant is not confined to denials of the allegations of the complaint or petition, but is entitled to set out new matter in defense or as a basis for affirmative relief. In a suit in which plaintiff alleges that defendant has been negligent, assumption of risk is sometimes a defense which a defendant can raise. In raising such a defense, defendant basically states that the plaintiff knowingly assumed the risk of the harm that was caused. The Second Defense of this form gives an example of pleading such a defense.
This form is a generic example of an answer and affirmative defense that may be referred to when preparing such a pleading for your particular state.