Bryce lies on the witness stand about his relationship with Hannah Baker by building upon the bogus story Marcus Cole told during his testimony. Bryce claims he and Hannah had "an on-again, off-again" sexual relationship that mostly took place at Hickman's Bridge where she would often talk about the frailty of life.
When asked if they ever had a committed relationship, he says he felt uncomfortable with the idea because Hannah had a reputation of being promiscuous. In addition, he claims Hannah wanted a deeper relationship and asked him for one the night of the hot tub party where they had sex. He goes on to say his refusal to persue a relationship spurred Hannah to claim rape.
This fake testimony has four major side effects. The first is an epic battle at school that starts as a brawl between Justin and Bryce but quickly escalates into a clash of good and evil as the jocks square off against the misfits. The second is that Chloe, Bryce's girlfriend, decides to testify on the Bakers' behalf. The third, and the creepiest, is that Bryce's mother confronts him about Hannah's assault, and he callously relays the truth behind the event. The last is that Bryce reflects on the very real crush he had on Hannah. We learn that the pair did take platonic visits to Hickman's Bridge where he was the one to use the landmark as a metaphor for the fleeting nature of life.
Unfortunately, Bryce doesn't get prison time. He's on probation temporarily, and he agrees to transfer to another school. Oh, and he's also (likely) the father of Chloe's unborn baby.