He joins us at golf (3)
I believe the answer is:
gus
'he' is the definition.
'us at golf' is the wordplay.
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'us' after 'g' is 'GUS'.
'joins' is the link.
(Other definitions for gus that I've seen before include "T. S. Eliot's theatre cat" , "Augustus (dim.)" .)