After hearing about the attempted rape, how does Owen's impulsive response put him at risk in the novel, Just Listen?

After Annabel confided in him, Owen was so angry with Will that he confronted him outside Bendo and hit him, giving him a black eye. This act of chivalry violates his probation and would have him back in jail if anyone lodged a complaint or called the police, but Owen is lucky. The worst thing that happens as a result is that his mother grounds him.