Definition of knock off:
, especially one of poorer quality
"this spreadsheet program is a knock off of Visicalc."
to bump or hit so that something falls off; to quit
; stop doing work or other activity. The term originated from the practice aboard slave galleys to have a man beat time for the rowers by knocking on a block or drum; when he stopped, the rowers could rest
"don't knock off the ornament with your clumsy arms."