In the first thing we see the kid is saying something about his mother. There is obviously more we did not see, the kid is not going to do this to some arbitrary figure. There is a reason the guys takes a while to react, why not just walk away? Because he knows the kid has a point to make and the man is not going to talk about it.
This is not some bad kid just being tough to a bigger grownup.
I agree, there is a back story here. The boy’s blocking behavior is similar to what I saw in my white wife’s very dysfunctional family in North Carolina. Both she and her daughter would engage in this sort of activity for extended periods of time. It is some sort of lower class rage filter behavior that enables the participants to be extremely aggressive without actually striking the other party. One goal is to provoke being hit so the cops can be called and the hitter goes to jail. It is very, very aggressive and disturbing behavior. note the adult male never struck the boy, he bidded his time and gave him a bump which caused the boy to fall straight down on a very hard surface. I did something similar with my big teen step daughter by letting her push me back to the bath room where I suddenly slammed the door in her face, she hit the door, lost balance and fell hard on the floor. Lots of squealing but no basis for a domestic abuse charge. Lower class people have developed a whole array of threshold of violence strategies to deal with their own internal demons generated by familial dysfunction