Cut loose, notice crack (6)
I believe the answer is:
adrift
'cut loose' is the definition.
(I've seen this before)
'notice crack' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'crack' becomes 'rift' (rift is a kind of crack).
'ad'+'rift'='ADRIFT'
(Other definitions for adrift that I've seen before include "'Directionless, floating freely (6)'" , "Loose from moorings" , "like Mary Celeste?" , "Floating uncontrolled" , "Unsettled or unanchored" .)