I was taught that the correct phrase for this was in fact "off your own BAT" as opposed to back.
Apparently something to do with cricket? Now it's always used as "back" but meaning the same thing. I.e off your own initiative. I'm not sure how it evolved, other than people mishearing the word bat?
Does anyone have any feelings on whether bat or back is the 'correct' terminology, or if both are now equally acceptable? Or maybe that the phrase in itself is ridiculous?
Really interested to hear people's thoughts!