Later, you can get fat on a half of beer (5)
I believe the answer is:
after
'later' is the definition.
(I've seen this before)
'a half of beer' is the wordplay.
'half' indicates taking half.
'beer' becomes 'ter' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'of' with half the letters taken is 'f'.
'a'+'f'+'ter'='AFTER'
'you can get fat on' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for after that I've seen before include "Coming later in time" , "Following, consequent to" , "Post, later than" , "Behind; in quest of" , "Subsequently" .)