I would imagine that they could pass legislation that, anybody who was not a citizen (i.e., on a visa, an invited guest of the Danes) and was arrested for any crime (including rioting), was subject to immediate deportation (without the right of return).
As a matter of fact, such legislation would be appropriate in any free society.
Guests don't get to come into your home and crap on the living room carpet.
It is a valid question, though, deportation to where? Country of origin, perhaps. But then they’d claim refugee status. That’s why I favor dumping them somewhere that they wear towels on their heads. If they won’t let them in at the port, smuggle them in somewhere along the coast. If their borders are too well patrolled, dump them a mile off shore.
They rioted. Their bad. Law-abiding, hard-working Muslim types are free to not riot and thereby stay in the country. If they can’t control their teenage sons, that’s their problem.
Write to your Danish People’s Diet-man.