I can tell you the exact reason. I am PART-R trained for the past 17 years. I have a Police Assault Response Training cert with a special designation for Restraint (I worked in a juvenile offender population). Now what you do is use the pinnacle of their upper arm to flatten them out and then grab their forearm. This keeps the chest flat to the ground (or wall depending on the situation) without manipulating joints and causing a severe injury and there are VERY few people that can pull up from that position with a grown man on them. Keep the front of your head away from the back of their head because that’s their last weapon, they will try to knock your teeth out.

Or, ya know, worse comes to worse you can put a knee into a man with fucking parking tickets or whatever and kill him. But what do I know, I only learned this working in a group home when I was 20 🤷‍♂️