There’s a Twitter thread with a lot of video. The event is the hill bomb, where skaters ride down the hill by Dolores park. This is legendary event in skate culture, since the 1980s at least.

Tweet by @aldot29

“Here’s another view of what’s going on here at Dolores. Some police pointing non lethal rubber bullet launchers at Hillbomb attendees.”

Here’s an article about hill bomb from 2019. This has been going on for decades, and is a celebrated event in the city. https://www.sfgate.com/bayarea/article/hill-bomb-San-Francisco-skateboarders-Dolores-St-14090264.php