WordNet sense 1 (be the defense counsel for someone in a trial):

represent, represent

WordNet sense 2 (protect or fight for as a champion):

champion

WordNet sense 3 (protect against a challenge or attack):

guard, hold

WordNet sense 4 (fight against or resist strongly):

fight, oppose, fight back, fight down

WordNet sense 5 (state or assert):

maintain

WordNet sense 6 (argue or speak in defense of):

support, fend for