Its not normal. even for fun.
I was pretty much the same at that age. Love violence. I've always been a sadist....
Definitely might want to get some clarification as to why...
It depends, has he been playing Violent Video games,Watching Violent Movies. He could just be Drawing what he has Seen.
Maybe he's being bullied by his friends or whatever.<br />
He's letting out his emotions and that's how he is doing it!
Better to draw it than do it