This move exists primarily or exclusively within the Sonic Boom continuity. Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
The Hammer Throw is an attack that appears in the Sonic Boom comic series published by Archie Comics. It is a combination attack between Knuckles and Amy where Knuckles throws Amy at the opponents.
When performing Hammer Throw, Knuckles grabs Amy around her ankles and spins around at high speed to built up momentum before throwing Amy into the opponent where she presumably deals a heavy hit with her hammer.