An arrest report from the Hillsborough County Sheriff's Office said Foster was booked into jail at 11:11 p.m. He is being held without bail.
Foster was arrested by Tampa police at 9:10 p.m. at the Grand Hyatt hotel, where the team is staying before playing the Tampa Bay Buccaneers on Sunday.
The 49ers didn't immediately respond to requests for comment. But general manager John Lynch and coach Kyle Shanahan said in April following a previous Foster arrest on domestic violence charges that were eventually dropped that the team had a zero-tolerance policy on the issue.
"We can promise you guys, if there's someone who ever hits their significant other, girlfriends, some person like that, that person is not going to be on our team,'' Shanahan said. "I feel strongly about that. I know John does. I know our ownership does. That's how we feel about it. Obviously, Reuben is on our team right now, so we're waiting to see how that goes. But, if that's something that we felt he did or ended up happening, you guys will see how we feel."
According to a statement released by Tampa police, Foster and a 28-year-old woman were involved in a verbal altercation Saturday night. The woman told police that during the altercation, Foster "slapped her phone out of her hand, pushed her in the chest area and slapped her with an open hand on the right side of her face," the statement said. Police said a 1-inch scratch was observed on the woman's left collarbone.
Police also said in the statement that Foster and the woman lived together in the past and had been involved in an "on-again-off-again relationship over the past three years."
Foster has had multiple run-ins with the law since being drafted by San Francisco 31st overall in 2017.
Foster was charged in January in Alabama with second-degree marijuana possession. That charge was eventually dismissed after he completed a first-time offender diversion course.
Foster then faced more serious charges for an incident at his home in Los Gatos, California, in February. He was initially charged in April with felonies for domestic violence, making criminal threats and weapons possession after being accused of beating up his ex-girlfriend.
A judge ruled there was no probable cause on the first two charges after the ex-girlfriend recanted the allegations and the judge found no other evidence to support the charges. The weapons charge was reduced to a misdemeanor and Foster pleaded no contest to that in June.
He was sentenced to two years' probation, 232 hours of community service and $235 in fines. He is not allowed to own guns while he is on probation.
After the charges were dropped, Lynch said Foster was told he would have to continue to earn his place on the team with his behavior.
Foster was suspended the first two games of the season for violating the NFL's conduct and substance abuse policies.
Foster has struggled on the field this season as he has dealt with shoulder and hamstring injuries. He had missed the past two games because of a hamstring injury and is listed as questionable for Sunday.
Foster has 29 tackles in six games this season with no sacks, forced fumbles, fumble recoveries or interceptions. He has also missed 10 tackles in six games, according to SportRadar, and has the second-highest rate of missed tackles among any linebacker with at least 200 snaps on defense.
The Associated Press contributed to this report.