who is the protagonist and the antagonist?

This is not straightforward. The 12 jurors share the play but Juror 8 is the one who presses for truth. If I were to pick one juror for a protagonist, I might choose Juror 8. Most of the other jurors want to just go home but Juror 3 seems the angriest an most uncooperative. We learn early on that he has a bad relationship with his own son, with whom he is no longer speaking. We are led to believe that this is a contributing factor to his prejudice against the defendant, accused of stabbing his own father. I might consider him to be the major antagonist of the group.