LEWISTON — An alcohol-fueled party for college seniors to blow off steam turned rowdy early Wednesday, leading to 11 arrests, an officer with a broken a leg and student complaints about police overreaction.

The gathering that began late Tuesday was part of a Bates College senior tradition called “return to your freshman dorm.”

Lewiston police were summoned by campus security after some of the 200 to 250 partiers declined to get out of the way of an ambulance that had been called to care for two injured women, police said. Nearly half of the group cleared out, but police said some refused to obey orders.

Officers never resorted to Tasers but used pepper spray after 100 to 150 students refused to disperse, Lewiston Police Chief Michael Bussiere said. He also said at least one officer displayed a baton.

“There’s a difference between use of force and excessive force,” Bussiere said.

During the frenzy of arrests, a police sergeant’s leg was broken in two places, Bussiere said. Samuel Guilford, a former Bates student, was charged with aggravated assault, the chief said.

Students accused police of being overly aggressive.

Paul Chiampa, a junior from Pembroke, Mass., said officers grabbed him by the arm while trying to get the partiers to disperse. He said he told an officer to “take it easy” and the next thing he knew a half-dozen officers were wrestling him to the ground.

“It was absurdly excessive,” Chiampa said today as he sat in a dining hall with his elbow on ice. He had abrasions on his cheek and the bridge of his nose.

All told, one woman and 10 men, including Guilford and Chiampa, were arrested. Most of the charges were for failure to disperse, disorderly conduct and refusing to submit to arrest.

This morning, the ground outside the dorm was littered with debris including beer cans and liquor bottles.

Tom Carey, director of security at Bates, said it’s too early to say whether the criminal charges will affect any seniors’ participation in Sunday’s commencement ceremony. The college, a selective liberal arts school with about 1,800 students, is conducting its own investigation into the episode, Carey told reporters.