As part of efforts to clean up UN Plaza, San Francisco authorities this week started work on clearing out unlawful activity at night.
In November, a large portion of the plaza was converted to a skate park, which has helped during the day.
The skateboarders usually stay through the early evening, but when they call it a night, a lot of the trouble that used to be focused at the site returns.
"I've been out there pretty late myself skating, but once people do go home and the positive activity is finished, it's unfortunate that unpermitted and people selling illegal items out there return," said Rene Colorado with the Tenderloin Merchants Association.
This week, a team made up of police, sheriff's deputies, probation and department of public works code enforcement agents swooped in on the nighttime illicit activity.
"Public health to get people help when they need it," police Chief Bill Scott said. "We have outreach workers out there at night. And we're really stepping up our efforts at night to try to shut down these illegal vending markets and people that are out using. Gotta deal with that as well."
Police said officers made several arrests Wednesday night, the first night of the new enforcement effort.
Scott said the nighttime enforcement is the next phase of an effort that started last year to crack down on open-air drug use and illegal sales in the area.
Get a weekly recap of the latest San Francisco Bay Area housing news. >Sign up for NBC Bay Area’s Housing Deconstructed newsletter.