Green’s Dictionary of Slang

(Aus. Und.) an act of barter whereby one criminal offers the police an alternative victim in order to evade his own prosecution for a crime.

1991

M.B. ‘Chopper’ Read Chopper From The Inside 105: The term for this is the ‘swap out’. When the police get close to Freddy he gives them the swap out; it has kept him out of jail for years. Two major drug dealers are in Pentridge now because of a swap out. They were given up by a middle man who takes his orders from Freddy.