Abandon half of crew in sub (5)
I believe the answer is:
scrub
'abandon' is the definition.
(scrub can mean to remove or delete)
'half of crew in sub' is the wordplay.
'half of' suggests halving the letters.
'in' means one lot of letters goes inside another.
'crew' cut in half is 'cr'.
'cr' inserted into 'sub' is 'SCRUB'.
(Other definitions for scrub that I've seen before include "Take out - clean" , "Stunted growth" , "Rub hard to clean" , "Wipe out" , "Brush, in two senses" .)