Subway acrobats are making waves in New York City. The New York City Police Department is taking measures to crack down on the acrobats performing on the subway trains.

Are the subway performances legal? Sometimes, not. More than 240 people have been arrested on misdemeanors related to acrobatics so far. Fewer than 40 arrests were made at this time of year in 2013, according to NY1.

Police Commissioner William Bratton acknowledges sometimes “low-grade lawlessness” can make more dangerous offenders bolder.

"Is it a significant crime? Certainly not," Bratton said recently, according to the Associated Press. But the question is, he added, "Does it have the potential both for creating a level of fear as well as a level of risk that you want to deal with?"

Officials involved with the NYPD’s Transit Bureau also said that if the dancers make a mistake, then someone could get hurt. NYPD is looking toward solo dancers as well as larger groups. Police have recently stopped groups of 12 from breakdancing and performing other acrobatics on the subway.

Good news though, for those determined to dance in the subway. If the dancers want to perform in the subway, they’ll need a permit.