What could I have done?

For context, I live at a taman built mainly for university staff with homes they can rent. Sometimes, when students aren't active enough (or in their last sem), they also rent out these staff homes.

There is a public park made too. Playground, a small empty field for football under a large tree that provides the most comfortable of shades.

However... it is also unfortunately directly behind a house with a steel back door. Only a short ass fence separates the house and the field. The pagar does nothing to stop a football.

I spend evenings with my little brother, watching him go main bola. Children, of course, being children, hammered the fully pumped ball into that door (one time that day, third time for the week) which would undoubtedly be loud from the inside. Then out came an abang-abang student. In an attempt to "assert dominance" and show their frustration, they banged the door as loud as they could in return, coming out shouting about being "reasonable" and warned them multiple times, then demanding the football be handed over to them.

It ended up with the ball owner (poor little guy) being intimidated and pressured by three large men to give in and hand over the ball.

Personally, I didn't do anything other than watch nearby, then felt bad when he looked so sad after. Abang student said they'll hold onto the ball for a few days to teach them a lesson.

I wish I could've helped in some way, maybe de-escalate instead of watching children being pressured to give their possessions to a stranger that's bigger and scarier.

I know I shouldn't have done anything drastic but damn, my guilty conscience is really speaking to me because the kids looked so bummed out. I hate the bystander effect... What do you think, korang?