Baseball fans are generally unaccustomed to getting their playoff games with a side of debate over police brutality, but this season supporters of convicted ex-BART cop Johannes Mehserle are giving them just that.

San Francisco’s AT&T Park boasts a waterfront promenade named McCovey Cove that opens onto China Basin where, for the last few weeks, Mehserle’s father Todd has been flying a banner that says: "Free Johannes Mehserle," and occasionally "Justice4Johannes.com." Mehserle was convicted of involuntary manslaughter this summer for shooting the unarmed Oscar Grant in the back and killing him. 

His father’s small protest wouldn’t be much of a big deal, but for the fact that the games have been aired nationally on Fox, which often pans to the Mehserle boat during the national anthem and during the league’s post-Sept.11 ritual of singing "God Bless America" at post-season games. At nearly every post-season game, the Mehserle banner has been seen flying in the wind with a large American flag attached to the top.

At a recent playoff game, Oscar Grant supporters arrived with their own banner, one large enough to obscure the boat it was hanging from.

"I thought the sign was inappropriate, but I have no problem with Mr. Mehserle supporting his son," the Grant family attorney Roland Burris told the San Francisco Chronicle‘s Chip Johnson. "In my view, it doesn’t mean anything more than that."

This weekend Grant’s supporters, led by the International Longshore and Warehouse Union, shut down ports in the East Bay to join a statewide day of action against police brutality.

Mehserle was convicted of involuntary manslaughter, the least serious of the charges against him, in June. The jury also attached a gun enhancement to his conviction. He faces anywhere from five to 14 years in prison, or as little as simple probation. Mehserle is set to appear in court for his sentencing on Nov. 5. At that time, Judge Robert Perry is set to decide on Mehserle’s other post-trial motions. Mehserle’s defense has requested a new trial for the cop.

The battle of the flags, meanwhile, will not likely abate soon. This weekend the Giants won the National League Championships and are headed to the World Series. The Texas Rangers will be in San Francisco this week for Game 1. Chances are, so will the banners.