Beer half-heartedly provided for nipper (5)
I believe the answer is:
biter
'for nipper' is the definition.
(something which nips)
'beer half-heartedly' is the wordplay.
'beer' becomes 'bitter' (bitter is a type of beer).
'half' indicates taking half.
'heartedly' becomes 'er' (I can't justify this - if you can you should believe this answer much more).
'bitter' with half the letters taken is 'bit'.
'bit'+'er'='BITER'
'provided' acts as a link.
(Other definitions for biter that I've seen before include "One may snap" , "One using teeth" , "Someone eating" , "Someone using their teeth" , "One cutting" .)