Reasons not good for sets of drinks (6)
I believe the answer is:
rounds
'sets of drinks' is the definition.
(a round is a set of drinks ordered at a bar)
'reasons not good' is the wordplay.
'reasons' becomes 'grounds' (grounds or reasons for an action).
'not' indicates named letters should be taken away.
'good' becomes 'g' (abbreviation).
'grounds' with 'g' removed is 'ROUNDS'.
'for' is the link.
(Other definitions for rounds that I've seen before include "lots of applause" , "Stages in a competItion" , "Circuits of the golf course" , "18 holes of golf and boxing bouts, say" , "Divisions of some contests" .)