Irrelevant. As I said, provocation is not a valid defence under UK law, it doesn't matter if the ball boy held onto the ball, refused to give it back and called his mother a dirty whore, it does not excuse assault.Physical abuse of snotty, game delaying ball boys is not a major concern. There's no way he's getting 8+ games. Also, I doubt a 17-year old really gets hurt that badly by what appeared to be a rather weak kick aimed at the ball.
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Also, regardless of whether it was a "rather weak kick aimed at the ball" (didn't look weak to me), there is no minimum level of force necessary to be classed as assault and battery. Also, aimed at the ball, again irrelevant, it would be argued in court that Hazard should have known there was a risk he might hit the person not the ball and so should not have done it.
Go watch more CSI because your post is full of fail