I'm not sure what background information you are supposed to know on this. Certainly any discord among the jurors makes tension. You need a collective jury to to hand down a verdict. These jurors are hot, tired, and upset. A group will naturally look favourably to strong evidence that will end the trial. Any discord could convince other jurors to change their mind and shift the group dynamics.
These jurors want to end the trial fast and give the judge the most obvious verdict. Which is "Guilty." However, the #8 juror opposes to the so called obvious verdict, so the others get upset and angry. This also triggers their wanting to have a reasonable answer to their discomfort. They continously show disrespect to the #8 juror redirecting the attention to some jokes and games showing their disatisfaction till the first big point is made. And it goes on shifting one by one to the otherside. However, the #8 juror started it because he only wanted to hear more about the boy's life and his circumstances. But as the conversation went on the small points made by others helped him think of ways to prove the kid "not guilty." Thats what I think.
The play is set in a New York City Court of Law jury room in 1957. The play opens to the empty jury room, and the Judge’s voice is heard, giving a set of final instructions to the jurors. We learn that this is a murder case and that, if found guilty, the mandatory sentence for the accused is the death penalty. After these instructions, the jurors enter. These are 2nd-12th Juror and the Foreman.
The men file in and decide to take a short break before deliberating. They talk casually and we begin to meet some of the jurors. They complain that the room is hot and without air-conditioning; even the fan doesn’t work. All who talk about the case seem flippant about the situation, and all presume the obvious guilt of the defendant, who we learn has been accused of killing his father. Eventually, the twelve sit down and a vote is taken. All of the jurors vote “guilty,” except for the 8th Juror, who votes “not guilty,” which, due to the requirement of a unanimous jury, forces them to discuss the case. The other jurors react aggressively to his dissenting vote, trying to quickly talk him out of it, but 8th Juror remains convinced that he is “not sure” whether or not the boy is guilty and feels that they owe it to him to talk about the case for at least an hour, just to make sure. He cites the boy’s troubled upbringing, with his mother dead and his father jailed. Jurors try to argue with him, most notably 10th Juror, who makes a particularly racist argument against the defendant, saying that “they’re born liars.” 12th Juror isn’t even paying attention, doodling an ad idea for his marketing campaign. Ultimately, they decide to go around the table, explaining why they believe the boy to be guilty, in hopes of convincing 8th Juror. Through this discussion we learn the following facts about the case: an old man living beneath the boy and his father testified that he heard upstairs a fight, the boy shouting, “I’m gonna kill you,” a body hitting the ground, and then he saw the boy running down the stairs. The boy claimed he had been at the movies while his father was murdered, but couldn’t remember the name of the movies or who was in them. A woman living across the street testified that she saw the boy kill his father through the windows of a passing elevated train. The boy had, that night, had an argument with his father, which resulted in the boy’s father hitting him twice. Finally, the boy has an extensive list of prior offenses, including trying to slash another teenager with a knife. 3rd Juror makes a speech about how this boy is just another example of “how kids are nowadays.” He speaks about his own son, with whom he had a rough relationship, and to whom he hasn’t spoken in two years, after a fight in which his son hit him. 10th Juror and 5th Juror get into an argument...