It's difficult to restrain a healthy adult without simultaneously endangering his life especially without unduly risking your own, except where you have a significant size advantage.

Consider it from an evolutionary perspective: a pinned animal is a dead animal. So we should expect animals to resist being trapped to the point of killing themselves / dying from the stress of fighting to break free. It's well known to be true for many animals and its also true for humans.

Anytime a person is forcefully restrained there is a risk of death.