Dykstra filed the suit seeking unspecified damages Wednesday against the county and several Sheriff's Department employees, saying his head was slammed against the wall, his teeth were knocked out and he was beaten until he was "barely breathing."
The alleged unprovoked beating occurred in 2012, when Dykstra was serving time for auto theft and charged with other crimes. He was released from prison last June.
Dykstra had a 12-year career with the New York Mets and Philadelphia Phillies.
The Sheriff's Department had no immediate comment, but when the beating allegations arose at a sentencing hearing, a sheriff's spokesman acknowledged a struggle, but said Dykstra had been the aggressor.