It's all very well to say that kicking the attacker in the head was 'cowardly' and 'dangerous'. But we have to remember that Jason is young, he was probably some degree of drunk, and he panicked. I'm sure he's not proud of it but I don't think many of us can say for sure how we'd react in that situation. He was watching his friend getting beaten pretty savagely and I can imagine that all his brain was able to compute was that he had to do something. Given time to think about it I can almost guarantee he would've acted differently. Besides, I'd much rather have seen that than a video of Jason standing around, watching, and taking no action.
As it happens I don't think he's good enough to make it with us, but this incident hasn't really made me think any less of him as a person.