I think he was holding his head because he was frustrated he just came back and he was hurt again and I think he could tell he knew the knee injury was bad. I think it was just out of anger/shock more than anything.
I felt so bad for him today, but I do have to say that as I watched them hit him I remember thinking "wow, they were careful to NOT hit him in the head. That was great!" and then scratched my head trying to figure out what was up until they got him up and I saw his leg. Poor kid cant catch a break!