Get away. Punches are controlled. The person being punched can determine if they are happy with the level. With someone running across multiple people what they get on their stomach is what they get. They have no say or control over it. It's not scaleable. Don't get me wrong. I'm pretty sure I could have a fairly heavy person standing on my stomach. But there are more combatively applicable ways of training to take a body shot without introducing that "what if" factor of some muppet stepping on people.