Many have to tee up, we gather (4)
I believe the answer is:
meet
'gather' is the definition.
(synonyms)
'many have to tee up' is the wordplay.
'many have' becomes 'm' (I can't explain this - if you can you should give a lot more credence to this answer).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'tee' reversed gives 'eet'.
'm'+'eet'='MEET'
'we' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for meet that I've seen before include "Come across" , "assembly at hunt" , "Proper; touch" , "Come together or run into" , "Get together socially or for business" .)