It’s a backpack bro.

 @janci1236: Dude srsly? Look at the guy sitting, his left knee is clearly in a Brace ????

 @LukasN89: Oh, thought you meant the guy standing on the very right, his backpack looks like some kind of figure eight brace to me. Did not noticed the knee, do not know, maybe he just have some issues going on with his knee and wears the brace for extra support, who knows.