except as provided 161.215 (limitations on use of physical force in defense of a person) & 161.219 (limitations on use of deadly physical force in defense of a person) a person is justified in using physical force on someone else for self-defense or to defend a third person from what they reasonably believe is the use or imminent use of unlawful physical force, & they may use a degree of force which they reasonably believes to be necessary for the purpose