Kenneth Carrethers, 43, claims Mehserle and the other officers violated his constitutional rights and injured him in a confrontation at BART's Coliseum/Oakland Airport station on Nov. 15, 2008.
The incident occurred six and a half weeks before Mehserle shot and killed an unarmed Hayward man, Oscar Grant, at BART's Fruitvale station on New Year's Day in 2009.
Mehserle, who said he accidentally used his revolver when he had meant to use his Taser stun gun, was later convicted of involuntary manslaughter and served about a year of a two-year sentence.
The current trial before an eight-member civil jury in the court of U.S. District Judge Edward Chen is expected to last about two weeks.
Carrethers is seeking unspecified financial compensation for alleged pain, humiliation, lost pay and medical expenses.
The incident occurred at about 10 p.m. as Carrethers was returning home from his job as a hotel engineer in San Francisco.
He claims that after Mehserle overheard him complaining that BART police were incompetent and failed to prevent vandalism to his car, Mehserle tackled him and then, along with the other officers, kicked and punched him, hog-tied him and carried him to a police car.
BART contends the officers used only reasonable and necessary force to control Carrethers after he appeared to be threatening violence.
BART attorney Dale Allen told the jury during his opening statement today, "Mehserle acted to stop an unprovoked assault on another officer."
The first witness called to the stand by Carrethers' lawyers was former BART Police Chief Gary Gee, who was questioned by attorney Christopher Dolan about the agency's policies toward riders who criticize police.
"People weren't supposed to get beaten for exercising their First Amendment free speech rights, were they?" Dolan asked.
"No, they're not," Gee answered.
Both sides have indicated they plan to call Mehserle and the other officers to the stand later in the trial.