San Francisco police detained a motorcyclist who they said drove his bike at a group of protesters demonstrating against the federal health care bill in an apparent attempt to hit them, according to witnesses as well as photographs and videos from the scene.

A few dozen people were staging a “die-in” early Wednesday afternoon on Seventh Street near Mission Street when the man on a red motorcycle appeared, said one of the protesters, 43-year-old Tracey Brieger of Emeryville.

She said the activists, some of whom held up posters that looked like tombstones to decry the Republican health care bill designed to replace the Affordable Care Act, had planned to block the intersection for about 10 minutes.

They had been lying in the street for about 7 minutes when a motorcyclist turned the wrong way on the one-way street and drove toward the protesters, witnesses said.

“He was revving and revving, he was gunning it, aiming at people who were laying down,” said Brieger.

The man was soon surrounded by police and detained, witnesses said. In video footage of the confrontation, officers appear to point weapons at him and order him off his bike.

Police Department officials did not immediately provide details on the case.

The red 2015 BMW motorcycle captured in photographs is registered to San Francisco resident Jeffrey Dillon, according to the California Department of Motor Vehicles. On social media, Dillon is seen posing with the bike and is the administrator of a Facebook group called the “White Privilege Club.”

“This isn’t a racist site/group, it is the exact opposite. It is a celebration of our culture and who we are,” Dillon posted on the group page.

“I am proud of who I am and my people,” he wrote. “The media and these social justice warriors are going to try to shame us with the words ‘white privilege,’ well we will throw it right back at them and wear it as a badge of honor.”

As the motorcyclist drove toward the people on the street, many rolled to the side to get out of the way, Brieger said.

“I thought he was playing chicken,” said 65-year-old Bruce Allison of San Francisco, who was also at the demonstration.

He said the motorcyclist yelled at the demonstrators, “If you want to go to the hospital, here you go,” as well as, “You will have health care if you people stop protesting.”

After the demonstrators rolled out of the way, the man made a U-turn and came back at them in the other direction, Brieger said.

After he was detained, she said, he told some of the protesters, “You guys were blocking the intersection and now you’re not. See how that works?”

Sarah Ravani and Filipa Ioannou are San Francisco Chronicle staff writers. Email: sravani@sfchronicle.com, fioannou@sfchronicle.com Twitter: @SarRavani, @obioannoukenobi