Getting a spanking from a cop after being subdued isn't going to instill discipline in a kid. It'd be pointless. Pepper spray was the best solution, since it stopped the kid, and didn't risk injuring him in a way the cops might get sued for, like a more physical takedown might have.
Discipline is something that takes time and consistency to permanently teach, no matter what methods you use. The only person who has enough control over that kid's life to teach it is, unfortunately, his mother. She won't, so as I said before, unless the kid is raised elsewhere (new family, boarding school for kids with mental issues), he won't learn. A spanking from a cop won't turn that around and stop him from being a future convict.
Hit And Run Poster Extraordinaire
--Too Dumb to Quit--