If there is rioting and looting shut down that city's team for a decade. If it happens a second time shut them down for a millennium. If the dirtbags, scum and trash are going to abuse the situation then reward them for it by shutting their team down.
In order to shut down a business enterprise like a professional sports team because of the rioting of the fans, you would have to prove that the business had the power to control the third party fans, or prove the team was directly responsible for the actions of its fans, including the ones who were not at the game. Good luck with that.
Pro sports teams are totally unnecessary.
Neither are hot dogs, apple pie and Chevrolet, but those things along with baseball is what America is all about, and if you don't like at least one of 'em you're not a real American. Can't be. No way.
It has been widely accepted that the 2001 World Series between the Arizona Diamonbacks and the New York Yankees played not an insignificant role in this country beginning the healing process in the aftermath of 9/11. Then again, they also said the same thing about Letterman and SNL. YMMV
In any case, "necessary" is a very subjective thing when you try and apply it to the following:
Economic Value of the Major Leagues
MLB *Gross Revenue: $2.79 Billion *Net Worth: $6.55 Billion
NHL *Gross Revenue $1.82 Billion *Net Worth: $3.75 Billion
NFL *Gross Revenue: $3.51 Billion *Net Worth: $12.80 Billion
NBA *Gross Revenue: $2.1 Billion *Net Worth: $6.01 Billion
You get rid of professional sports, you put an awful lot of people out of work. And I don't mean the athletes.