Definitions by Dante De Rossi

head stock swing 

the act of taking the neck of a guitar and/or bass and outwardly swinging the instrument it to the side, making the guitar or bass perpendicular with the body violently (left or right depending on playing style) then pulling it back violently while keeping the song going.

That band had some badass head stock swings during their breakdowns.

head stock swing by Dante De Rossi October 19, 2006