Wes runs to get a knife to send the kid who punched him a message by threatening or possibly cutting him.
When Wes is eight, he's playing football when an opponent punches him in the face. Wes had been guarding him closely and refused to let up when the boy told him to. The boy then pumps his chest against Wes and they argue; the boy then punches Wes in the face. It was the first time he was ever punched in the face.
His friend Woody tries to stop Wes from retaliating, but when Wes tastes his own blood, he runs home to get a knife. He remembers the words of his brother Tony, who said:
If he ever slackened, Tony would pull an exhausted Wes to the side, get within inches of his face, and say, "Rule number one: If someone disrespects you, you send a message so fierce that they won’t have the chance to do it again." It was Murphy Homes law and Wes took it to heart.
The police catch him approaching the boy with the knife and take him in. It's his first arrest. He ends up calling his dad to pick him up because he doesn't want his mom to know what happened.