Falling off (8)
I believe the answer is:
slippage
'falling off' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slippage that I've seen before include "falling away from a standard" , "Failure to reach a set target" , "sliding" , "Lag pipes (anag)" , "Failure to meet target" .)