A Boston police officer filed a federal lawsuit yesterday asserting that a state trooper slapped him and dragged him at least 150 feet with his cruiser during a dispute outside TD Banknorth Garden in 2006.

Edward J. MacPherson, a 20-year veteran of the Boston police force, said in the civil rights suit that Trooper Robert Grover attacked him for allegedly failing to keep traffic moving as MacPherson worked a paid detail during a Tim McGraw and Faith Hill concert.

He said Grover bumped him with his cruiser, slapped him in the face, and knocked his police hat off, and then dragged him as MacPherson's arm was wedged in the window, causing him to lose his handcuffs, police radio, and the ammunition clip in his gun.

"Here's a police officer on duty," MacPherson's lawyer, Peter T. Marano of Boston, said of his client last evening in an interview. "He can probably rationalize a bad guy trying to hurt him. How do you rationalize someone in a police cruiser and a uniform trying to do that to you?"

MacPherson was taken to a hospital afterward with injuries to his left shoulder, arm, and back. He was out of work for several months after the confrontation, which drew little news coverage, and suffered from post-traumatic stress disorder, his lawyer said.

Marano said the State Police subsequently held a court martial for Grover. He said he did not know the outcome, but added that Grover is no longer employed by the State Police.

Sergeant Robert Bousquet, a State Police spokesman, said Grover has retired, and he did not know whether the episode with MacPherson was a factor.

Bousquet said he could not comment on whether Grover was subjected to a court martial because such proceedings are personnel matters.

The episode began shortly after MacPherson arrived at Causeway and Beverly streets at 10:25 p.m. on June 26, 2006, to help pedestrians cross and to keep traffic flowing, according to the suit. He was working outside his cruiser.

Grover, who was assigned to the State Police Marine Unit around the corner on Beverly Street, drove up in a cruiser while wearing a T-shirt and shorts and told MacPherson that limousines were blocking the area and to move them, the suit said. MacPherson told him he would take care of it.

The trooper and police officer then argued, and Grover threatened to arrest MacPherson, the suit said. Grover then got out of his car, walked up to MacPherson, and slapped him in the hand. When MacPherson warned Grover not to touch him again, the trooper allegedly replied, "I'll be back, pal," then sped off in his cruiser.

About 20 minutes later, MacPherson was directing traffic when Grover, now in uniform, sped in his cruiser directly at MacPherson, the suit said. The cruiser skidded to a stop but bumped MacPherson, knocking him back several feet.

After MacPherson went to the window, Grover slapped him in the face, MacPherson said in the suit. MacPherson reached into the car and grabbed Grover's shirt, but the trooper gripped MacPherson's arm and stepped on the accelerator, dragging him down the street until the police officer fell to the ground.

Grover and several other troopers tried to place MacPherson in handcuffs, but stopped after several Boston officers arrived, said Marano. No charges were filed.

MacPherson's lawsuit names Grover, the State Police, and several State Police officials as defendants. The complaint alleges that Grover had a history of misconduct that his employer covered up.

Jonathan Saltzman can be reached at jsaltzman@globe.com.

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