Reason to go about half-time (6)
I believe the answer is:
motive
'reason' is the definition.
(I've seen this before)
'go about half-time' is the wordplay.
'go' becomes 'move' ('move' can be a synonym of 'go'**).
'about' is an insertion indicator.
'half' means to take half the letters.
'time' cut in half is 'ti'.
'move' placed around 'ti' is 'MOTIVE'.
'to' is the link.
(Other definitions for motive that I've seen before include "Reason for doing something, perhaps a crime" , "Reason (for acting)" , "What induces one to take a certain action" , "Underlying intention" , "Ground" .)