After Joe's brother got beaten up by an older boy at school, Joe gets revenge on the bully by urinating in his food and serving it to him. The bully starts eating his contaminated food. Nothing else happens.
When the protagonist broke into his employer's home to steal a cash box, he pushed an elderly man down the stairs when the man caught him.
In the very beginning of the movie, young Joe pokes a girl in class and the teacher responds by pulling his pants down and spanking him. His backside is momentarily visible during the punishment.
The father is very abusive to the family throughout the film and hits Joe frequently. There is reference to the mother getting beaten around as well. A kid cuts his ankle pretty badly. We see that a boy has been beaten up. A man roughs up another man over money that hasn't shown up.