So New York skaters do something every year called the Broadway Bomb. Essentially, they skate down broadway from 116th street to Bowling Green, the entire length of Manhattan.
On one level it's just Skaters having fun, but on another level they draw attention to the lack of good bike lanes and pedestrian throughways that run the length of the island. You can't bike or skateboard on the sidewalk, and for good reason, you'll knock someone over.
So skateboarding and biking in the street is technically legal, except for when they're skating down the wrong side of the street. That doesn't mean that the NYPD doesn't try to stop the legal activity.
And they usually fail.
Here's a fun video of skateboarders with a complete disregard for the NYPD and their net: