That's probably because you are confusing a 'jackle' with a 'jackal'
Jackal being an opportunistic scavenger.
I believe the term started in Australia (that's where I first heard it being used) and possibly around the Brumbies. Jackal-ing for the ball was a specialty of George Smith when others weren't really using the technique and a method of adapting to the change in Law interpretation where prior to that period the ruck was an area for feet, not hands. Hands were likely to suffer damage if they went near the ball at a breakdown in the good old days.
It was around 2004 IIRC that the use of feet died out. I recall John Mitchell as coach of the ABs copping a lot of flak in NZ as he changed style to remove the use of feet (as it was getting penalised more and more) before other teams did. Probably a little too early as it transpired.