If you have to pick a main antagonist for this movie, Juror #3 is your man. We can tell from early in this movie that #3 is a guy who's rigid in his opinions and not used to having people disagree with him. Even before the jury has started talking, he says, "Six days. They should have finished it in two. Talk, talk, talk. Did you ever hear so much talk about nothing?"
In this guy's mind, it's totally clear that the defendant is guilty, and he resents the fact that the trial gave so much time for the lawyers to make their arguments. At this point, though, even he is willing to accept the fact that this is the law, saying, "Everybody gets a fair trial. That's the system. Well, I suppose you can't say anything against it."
The longer this movie goes on, the more we learn about the reasons behind Juror #3's hate for the defendant. For starters, he clearly doesn't like the idea of a child killing his own father, which we can see when he says, "Well [Eighteen is] old enough. He stabbed his own father four inches into the chest. They proved it a dozen different ways in court. They proved it a dozen different ways. Do you want me to list them?" But it's still going to be a little while longer before we figure out just what this guy's hang-ups are.
What's This Guy's Deal?
It's not until Juror #3 starts talking about his own son that we see the true reason for his bias against the defendant. While thinking about the trial, #3 talks about how he once saw his own son run away from a fight. As #3 tells it, "I told him [my son] right out, 'I'm gonna make a man out of you or I'm gonna bust you up into little pieces trying.' When he was fifteen he hit me in the face. He's big, you know. I haven't seen him in three years. Rotten kid!" So it's clear now that this guy has a bit of a problem with kids not respecting their fathers.
Juror #3 doesn't like to be questioned, which is exactly why he'd like to punch Juror #8 in the face if he ever got a chance. By the midway point of the movie, #3 jumps up almost every time #8 speaks and says something like, "I've got a good mind to walk around this table and belt him one!" Eventually, he even gets to the point where people have to hold him back from #8 while he shouts, "Let me go! I'll kill him. I'll kill him!"
Watch Him Crumble
It's probably guys like Juror #3 who become brutal dictators, both for families and entire countries. And that's one reason why we need democracy to make sure people like this don't get to run things. When asked if he'd like to be the one to kill the eighteen year-old defendant, #3 doesn't hesitate to say, "For this kid? You'd bet I'd like to pull the switch!" So it's clear that there's a lot more on this dude's mind than just justice.
This is a guy who simply can't handle a world that doesn't do whatever he tells it to. That's why he gets so upset with Juror #8 and even threatens to resort to violence to get his way.
By the end of the movie, Juror #3 stands alone in his Guilty verdict. But he seems like a fire that's starting to burn itself out as he rants and says, "You lousy bunch of bleedin' hearts. You're not gonna intimidate me. I'm entitled to my opinion. Rotten kids... You work your life out!" But at some point in this speech, we see the energy drain out of him. After all, it's hard to be mad all the time without getting tired.
In the end, Juror #3 seems to go with a Not Guilty verdict out of sheer defeat and tiredness more than any sense of justice. But who knows? Maybe the other guys managed to change his mind a little bit.