Best thing to do is to make sure the switch in front of the hulk is super sensitive. The ball gets stuck when it rolls over the edge of that switch and makes it around his arm. When the switch is set real sensitive it will trigger a hulk hit and will also make him move around thus preventing the ball getting stuck.
It will still happen periodical though. Some people have raised his arm but I wont do that as by raising his arm to prevent the potential hang up makes obtaining the Hulk Super Jackpot much easier as his arm isn't blocking the shot anymore.
If it really drives you nuts some people have put a button in the tournament button slot that is connected to the hulk switch so you can just press the switch to activate the hulk if a ball gets stuck. After adjusting the switch real sensitive it happen rare enough on my game to where it doesn't bother me much anymore.