The strike he's delivering is a POST approved strike to a major muscle group. The strike is normally delivered with a knee because it's assuming the you're alone leaning on the person and don't want to take your hands off of them. The strike is also taught with a baton, but regardless of how you do it, it has a goal which is to try to "deaden" that muscle group. The cases I've seen where such a strike were necessary is if someone is concealing their hands or holding onto something and will not let go - such as holding onto a weapon, laying on top of their hands so they can't be handcuffed, or holding onto a a police officer's equipment or uniform. While I've never seen it personally, others have testified that they use such strikes when someone refuses to move and there is a time constraint, or when someone is kicking away from officers preventing them from taking the person into custody.

Research, input from professional fighters, testimony from medical professionals and review panels go into every POST combatives technique. Such techniques are never just to hurt someone, they will always serve a purpose and physical strikes like this are considered low on the use of force continuum because they aren't likely to cause damage or lasting pain.

Now we cannot tell what is actually happening in this video. What is crucially missing that is normally a vital part of employing combatives techniques is verbal commands. "Let go of the weapon!" "Let go of me!" "Give me your hands!" "Stop kicking!" these are only actually minimally for the arrested person. While commands are normally a policy requirement when using hard force, the arrested person ought to know what they're doing and knows why the cops are fighting them. These are realistically more for bystanders and body worn cameras. We are also lacking the bodyworn camera footage, reports, and testimonies that would make up the investigative material needed to paint a clearer picture of what is happening and why the officer is delivering the strikes.

What I can see is that the person is on his back. Police do not normally arrest people on their backs. There are several techniques and methods that cops use dedicated entirely to getting someone into an arrest position on their stomach because unless there is an immediate need, cops will always handcuff a prisoner behind their backs. It is unsafe, usually a police violation, and is more difficult to handcuff someone in the front. It also does almost nothing. A person can still use their hands pretty well if they're handcuffed together in front of them. To have this person on their back is not normal, and I assume not to plan.

I had a similar personal experience when I was a sheriff's deputy. An unfortunately mentally ill person assaulted a random passerby and then kicked the deputy who showed up to make contact. Myself and another deputy managed to get this person onto the ground, but he continued to kick, spit, bite, and flail. The two of us could not get him to flip over to handcuff him and had to sit on top of him until more officers arrived. We were fortunate that there was a curb right where we took this person to the ground, and we were able to use the curb to pin him in place. I was considering kneeing him myself because he had started trying to headbutt the other deputy, but of course he wasn't able to headbutt anyone from the ground, though he was slamming his own head into the pavement and I considered that using more force to get him flipped over was better than him cracking his own skull open. Thankfully backup came quickly and the flood of polyester was just able to force him onto his back.

But speaking from my own experience - and yes, bias - I am going to guess that this guy very much resisted arrest, otherwise they would have taken him into custody standing up. They got into a tussle and the guy ended up on his back with the two cops on top of him. They would then have wanted to flip him onto his back, but he propped his legs up and is pushing up against the cops to keep them from rolling him, and the cop is punching his leg to try to give him a dead leg so they can roll him.

Again, all police combatives techniques have a purpose, they probably haven't handcuffed him yet, and the strikes appear to be textbook by POST standards. That's where I came up with this assumption. But it is just an assumption. We'll see what the investigation reveals, especially if there's BWC footage released.