You seem to think he’s still sitting there and the police are still beating him

What makes you think that?

After I pointed out that he was pulled to the ground when he tried to get up and walk away, you said:

Now they should have given him a chance to walk away again but that isn't a requirement.

So clearly you're agreeing that they wouldn't let him leave. Then you changed your tune and said:

They didn’t prevent him from leaving.

But a police officer clearly pulls him back down on to the ground after he gets up to leave. That officer prevented him from leaving. Your statement "they didn't prevent him from leaving" was false. A police officer preventing the man from leaving is an event that occurred. It's shown in the video. I don't understand why you can't accept that what you said was wrong. You're acting like a child.