Just after 7 p.m. units tried breaking up a large crowd and say people started throwing things at officers. Two cruisers were vandalized.
One officer was injured and taken to the hospital.
VIDEO: Skateboarder collides with SFPD officer near Dolores Park
Officers tried to block skaters on the street with their patrol cars. One person tried to skate around them and flipped over. At one point officers let the crowd continue to skate.
At least one skater was also rushed to the hospital. Local artist Matt "Milanoart" shared video of what he says is Jake Phelps, editor of "Thrasher" magazine taking a nasty spill.
The whole scene ended about two hours after police arrived.