It takes Jay a second to realise what's going on and by the time he reacts to R's attack, R's already got a handful of his sleeve. Jay jerks his arm away and stumbles backwards. The sleeve tears. Jay, free of R now, takes a couple more steps back, then turns around and runs. He's in deep shock -- weren't he and R friends? Wasn't he going to help him? What happened?

He takes one cautious glance backwards, without slowing down. Maybe the attack was R's idea of a joke?