Withdraw from a commitment (4,3)
I believe the answer is:
back out
'withdraw from a commitment' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for back out that I've seen before include "Withdraw from agreement, or reverse car from driveway" , "in the open air again?" , "Get cold feet" , "Withdraw from agreement in outback" , "Withdraw from a commitment" .)