Flat foot is a slang term used for a policeman.
Rooster: He ain't gonna tell you nuthin'.
Baretta: How do you know he ain't gonna tell me nothin'. You so smart dealin' out info for twenty dollars a lick, go get loved.
Rooster: See ya later BIG TIME.
Rooster: Now you talkin'.
Baretta: You talk.
Rooster: Well you know this character Ricky Parrish you talkin' about.
Rooster: Ain't no sense in lookin' for him no more.
Baretta: How come?
Rooster: Word is he got snuffed.
Rooster: Hey man, that's the way it goes man, here today, gone tomorrow. Hope he had a righteous good time while he was here.
Baretta: (to Sue) My dad was a con and I promised him I'd become a flat foot and that's the name of that tune.