I HATE these PI's on the underthrown balls. Because there isn't anything the defender can do against it. If you are running step for step with a guy and he suddenly stops on a dime, turns around and tries to run back the other way you are gonna run over him. That's just how it is.
For all the attention the fumble out if the end zone rule gets,this is actually what drives me nuts. It rewards a very poorly executed play with game changing yardage