I had to physically restrain a 9yo once. His mother had called us as he was physically attacking her and she wasn't strong enough to stop him. It took two officers and the mum to restrain him, he was the strongest little thing I'd ever seen. We'd tried all the communication we could, he was destroying her/their house and had been attacking his mum, she'd called us in hysterical tears, it was one of the most unsettling things I've ever attended. (He had undiagnosed adhd and she was desperate for help, she was under cahms I think but awaiting a diagnosis.)
We didn't cuff him. We just had to physically restrain him. He was throwing things at us, brandishing a broken snooker cue at us when we arrived, and was kicking and punching us when his limbs weren't being held. Oh and biting. It took hours for him to calm down.
I'm sure us being there and trying to restrain him was making it worse for him, the poor thing, but what should we have done? He was trying to hurt people. His mother wanted us to take him away to begin with, but once he'd calmed down I think she agreed to stay with him and I think the people who took over from us organised an emergency appointment with cahms?
But we weren't doing anything to 'punish' him.
I haven't watched the video, so I'm sorry if this is irrelevant, I'm just trying to offer another perspective.