What does three do to eight in the beginning of act 3 that causes the others to cry, "look out!" How is this also an example of situation irony?

Juror Three attacks Juror Eight. This is an example of situational irony because only a short time before, all of the were united in their opposition of Juror Eight's views. At this point, they have all come around to the 8th Juror's point of view.... everyone except Juror Three, who now stands alone.