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LOS GATOS — The domestic-violence arrest of San Francisco 49ers linebacker Reuben Foster stemmed from his girlfriend’s accusation that he physically dragged her during an argument at a Los Gatos home Sunday morning, according to sources familiar with the investigation.

The reported victim, who has been in a relationship with Foster for several years, also told police dispatchers during a 911 call that he owned multiple semiautomatic rifles, according to an archived recording. Officers ended up recovering one firearm, a SIG Sauer 516 short-barreled rifle, sources said.

The encounter left the woman injured, sources said, but the extent of her injuries was not disclosed.

Altogether, the allegations were the basis of Foster getting booked at the Santa Clara County Main Jail on suspicion of domestic violence, making criminal threats, and possessing an assault weapon. He was released Sunday evening after posting $75,000 bail.

Foster’s agent did not immediately return a message seeking comment to the accusations. Foster has not commented since the arrest, including on his frequently-used social-media channels.

On Monday, Foster visited the 49ers training facility in Santa Clara to meet with team officials, according to Ian Rapoport of the NFL Network. Sunday evening, the 49ers sent out a statement acknowledging Foster’s arrest and that it is “gathering all pertinent information” in the case. The NFL is also conducting an investigation of the case to determine any potential suspensions and penalties from the league.

In 2014, amid criticism of its handling of the infamous Ray Rice case, the NFL gave Commissioner Roger Goodell authority to give players a minimum six-game suspension for domestic violence allegations, even without a conviction. That was exercised with star Dallas Cowboys running back Ezekiel Elliott this past season.

Because Foster is free on bail, he will not likely be charged or arraigned within the typical 72-hour window for jailed suspects. On Monday, Los Gatos-Monte Sereno police forwarded their investigation to the Santa Clara County District Attorney’s Office for review.

Prosecutors will have up to 30 days to decide on whether to file charges against Foster. All three offenses for which he was arrested are known as “wobblers,” meaning that if they are charged, they can be filed as either misdemeanors or felonies based on the discretion of the District Attorney’s Office or a Superior Court judge.

The criminal threats allegation, if charged as a felony, would count as a strike under the state’s “Three Strikes” law.

“The severity of the crime, any injuries, and prior criminal history factor into whether a charge gets reduced to a misdemeanor,” said Steven Clark, a legal analyst and former Santa Clara County prosecutor.

Clark added that it’s also not a certainty that prosecutors will file charges based on the initial investigation.

“The DA may ask for more information, such as whether there is a previous history of domestic violence, or if alcohol and drugs were involved,” he said.

A statement from Los Gatos-Monte Sereno police says officers were dispatched around 9:15 a.m. Sunday to a home on Shannon Road for a welfare check and to respond to a possible disturbance. Foster was eventually arrested without incident.

Police did not release any additional details, but sources familiar with the investigation say the victim told officers that she and Foster were arguing and that he threw her belongings onto a front walkway and balcony. At some point, she said he physically dragged her in an apparent attempt to remove her from the home, sources said.

According to an archived police dispatch radio recording of the 911 call, “the RP (reporting party) advises there should be at least two AR-15 weapons in the house.”

Both that statement and the domestic-violence allegation would provide cause for police to search for and remove any firearms from the home. It was apparently during that search that officers found the allegedly illegal rifle.

The weapons allegation against Foster evoked memories of the 49ers’ experience with former star linebacker Aldon Smith, who was given probation after being convicted of possessing three illegal assault rifles after gunfire erupted at his home in the San Jose hills in 2012.

Like in that case, the weapons allegation could take some time for prosecutors to sort out. For starters, the legality of possessing the SIG Sauer 516 short-barreled rifle will likely be debated between them and Foster’s legal defense.

The 516 does not appear on the list of illegal AR-15 variants at the California Department of Justice website, perhaps because it’s a recent release — the list hasn’t been updated in more than a decade; the 516 has been produced since 2010. State law also includes generic characteristics that make a gun illegal, such as whether it has the capacity to accept a detachable ammunition magazine, and at least one of a list of military-style characteristics like “a pistol grip that protrudes conspicuously beneath the action of the weapon” and a flash suppressor.

“It can sometimes be difficult to determine when you’re in possession of an illegal weapon, and these characteristics are difficult to know,” Clark said. “You have to find out if it was properly stored, was there ammunition inside of it. Was it just sitting inside a closet or was it being used? How did he obtain it?”