One gripping beer half-heartedly (5)
I believe the answer is:
biter
'one gripping' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'beer half-heartedly' is the wordplay.
'beer' becomes 'bitter' (bitter is a type of beer).
'half' suggests halving the letters.
'heartedly' becomes 'er' (I can't explain this - if you can you should believe this answer much more).
'bitter' cut in half is 'bit'.
'bit'+'er'='BITER'
Can you help me to learn more?
(Other definitions for biter that I've seen before include "Vicious dog perhaps" , "Someone using their teeth" , "He who is sometimes bit" , "Someone eating" , "One may snap" .)