Yes. But, problems.

 (1) His only way of proving it is to do one of two things - either have someone claim to have seen it (they'll have to prove they were there) and that someone be an "independant witness", or show videotaped evidence. Problem is, probability falls outrageously on the side that he has neither resource available.

 (2) As others have stated, negligence only applies to certain situations. This situation most likely doesn't fit that, especially since there are waivers at most ski resorts that basically make you state that you understand stuff like this will happen. These waivers only directly protect the resorts themselves and not the people you collide with, but they can also prove that the man knowingly and willingly took the risk of this boy colliding with him and injuring him.

 As I said, he has no grounds.

1) I didn't say proving it would be that easy however on a Ski resort I don't think finding even two witnesses would be that difficult.

2) The resort and any liability waver signed by the man in regards to the resort have nothing to do with this. It is a binding agreement between the Skier and the resort only. Consider this example: If a spectator runs up to a boxer during a boxing match and severely beats him, is the boxer unable to sue because of the waiver he signed in order to box? Of course not, it's unrelated.

That example is entirely and completely different, though. Did the boxer's waiver explain that the boxer WILL likely be attacked by a spectator? No, of course not! His waiver explained that ANOTHER boxer will be attacking him, and in the ring!

The waiver you sign at a ski resort explains that stuff like this will happen. Like I said, they only directly prove that, but I guarantee the lawyer can effectively use it as a part of the defense's case.

As for finding two witnesses, I'd agree it wouldn't be that difficult... if it'd happened fairly recently. But it's been almost a year. I highly, highly doubt anybody will remember it anymore, much less be even locatable.