What he needs is serious help. There's obviously something very wrong with a 13 year old who doesn't know the consequences of hitting someone in the head with a baseball bat. And according to reports, this isn't a "he swung in defense and did more damage than intended." He hit this kid 3 times, the 3rd time square in the head with a lot of force. One witness said (spiler tags, 'cause it's a little graphic)
I was bullied a lot as a 13 year old. I fought back occasionally as a 13 year old. But I understood what swinging a bat full force at someone's head would do. So either he was fully aware of what he was doing and should be punished severely, or more likely he lost control of himself with very little provocation (the article says that while he was being teased, the two didn't have any sort of history of problems, so it's not like it built up to it) and needs to be given a LOT of help to control that, because at 13 years old, you should be able to avoid going into a murderous rage.