Do a favor for (6)
I believe the answer is:
oblige
'do a favor for' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oblige that I've seen before include "Put oneself out for" , "Compel - do favour to" , "press!" , "Compel (someone to do something)" , "Coerce or accommodate" .)