Rescue Ali knocked out in fight (4,3)
I believe the answer is:
bail out
'rescue' is the definition.
(I've seen this before)
'ali knocked out in fight' is the wordplay.
'knocked out' is an anagram indicator (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'fight' becomes 'bout' (as in a bout in boxing).
'ali' with letters rearranged gives 'ail'.
'ail' put into 'bout' is 'BAIL OUT'.
(Other definitions for bail out that I've seen before include "Rescue from tight spot" , "escape from aircraft" , "finance in a tricky situation" , "extricate one from a difficult situation" , "Withdraw" .)