Is that legal and they cause a lot of social problem or something?

Well, I imagine they would.

The trick in Trick or Treat is mostly just a playful part of the tradition.

In reality, children rarely play tricks if they don't get candy.

Instead, they simply move on to the next house.

It's more about the fun of dressing up and collecting treats than causing any trouble.

As for legality, playing actual tricks, especially those that cause damage or harm, would indeed be illegal and is not condoned as part of Halloween celebrations.