Didn't happen to me so I can only pass the info I have on.
SM v LV at the weekend. SM set up a LO near half way and for the sake of this discussion the LO is set, static receivers... (i.e. no dynamic pre-throw movement).
Hooker throws the ball in and as the ball is leaving his hands the SM prop peels off and starts to run on an arc behind the receiver (say 5m away). Ball is tipped down to the receiver and then the dynamic prop receives a pass from the receiver and steams forward.