Two San Francisco 49ers season ticket holders beaten in a Levi’s Stadium restroom by two intoxicated brothers during a game last October have sued the team and the city of Santa Clara’s stadium authority, blaming them for failing to take security steps to prevent drunken violence during NFL games.

In a lawsuit filed Friday in Santa Clara County Superior Court, Kiran and Amish Patel, cousins who attended the game against the Kansas City Chiefs last year, contend the 49ers security efforts did not address the potential for violence from drunken fans, “creating an unreasonable risk of injury.” The two Central Valley brothers who committed the attack, both of whom were charged with assault, beat the two men so badly that one wound up in critical condition and underwent skull surgery in an incident captured on videotape by a bystander.

The lawsuit also alleges that the 49ers were on notice that there is a heightened potential for violence at NFL games, even citing the team’s own “pattern of criminal and violent behavior” by players — a reference to the 49ers recent spate of players facing legal troubles for off-the-field problems.

The lawsuit targets an issue that resurfaced again earlier this month, when another video after the Monday night season opener against the Minnesota Vikings captured 49ers fans beating a Vikings fan in the stadium parking lot. Santa Clara city officials are exploring options for dealing with such threats, including the possibility of stricter limits on alcohol consumption during games.

In the incident involving the Patels, Santa Clara County prosecutors charged two reputed gang members, Dario Rebollero and Amador Rebollero, in the attack, which occurred in a restroom just before the kickoff of the team’s game against the Kansas City Chiefs. Amador Rebollero pleaded guilty to two felony assault charges and was sentenced to five years in prison this summer.

A video, posted to YouTube after the incident, showed a man wearing a Frank Gore jersey throw three punches at another 49ers fan wearing a Colin Kaepernick jersey inside a crowded restroom. The man wearing the Kaepernick jersey falls to the ground and lies motionless as other fans stand and watch.

The lawsuit seeks unspecified damages, indicating both Patels are incurring ongoing medical costs as a result of the assault.

A 49ers spokesman declined to comment on the lawsuit. But after the incident, they issued a statement saying: “We were appalled to see the video of the attack on the victims and salute the Santa Clara Police Department on their quick response that resulted in the apprehension of the two suspects. Maintaining the safety of all stadium guests is our highest priority, and we are dedicated to providing a friendly and welcoming environment for any event held at Levi’s Stadium.”

Howard Mintz covers legal affairs. Contact him at 408-286-0236 or follow him at Twitter.com/hmintz