To make or keep safe from danger, attack, or harm. Sports To attempt to prevent the opposition from scoring while playing in or near (a goal or area of a field, for example). Sports To be responsible for guarding (an opposing player). Sports To compete against a challenger in an attempt to retain (a championship). To support or maintain, as by argument or action; justify. Law To represent (a defendant) in a civil or criminal action. Law To attempt to disprove or invalidate (an action or claim). To make a defense. Sports To play defense.