the stall is cramped and with three people standing there isn't really any space. Stalls here in the US the walls are 2 to 2.5 feet off the ground. Sam could drop, cover his face and roll under that. he wouldn't have to worry about being kicked since there wouldn't be enough room to wind up. That leaves two men in a stall and sam with a clear dash to the door. When Sam drops to roll out the assailents would probably take it as a cue to attack so the would focus their movement into the stall and it would take too much time to reposition and leave the stall before Sam opens the door.