I was defending a friend in a fight and....?

Basically, we were at the beach. Me and a bunch of friends. Some chavs from our school walked by and started throwing sand and rocks at us (me in particular) when my friend - lets call him Tim - gets fed up and goes over to tell them where to go. One of the chavs, he can be called Kyle, grabbed him and started punching in in the face and head for a no reason. Tim was helpless and no one was helping so I instinctively ran over to get Kyle off Tim. It was a struggle and all I could think to do was claw and bite at Kyle's back. I was in a blind rage and nothing could stop me until Kyle threw me off and was moving towards me when 2 strangers come over and restrain him. Anyway, a few weeks later its all over the school and Kyle had been showing people his back and photos were going round of it. The wounds are pretty deep and it looks like he's been whipped multiple times - all where i had scratched. My nails arent particularly sharp or long but those marks were definately made by me. Can anyone tell me how I managed to inflict these injuries without me even being properly aware?