Man on wagon seen in AA meeting (7)
I believe the answer is:
regatta
'meeting' is the definition.
(I've seen this before)
'man on wagon seen in aa' is the wordplay.
'man' becomes 'reg' (short for Reginald).
'on wagon' becomes 'tt' (I've seen this in other clues).
'seen in' indicates putting letters inside.
'tt' inserted within 'aa' is 'atta'.
'reg'+'atta'='REGATTA'
(Other definitions for regatta that I've seen before include "It could involve a lot of rowing" , "Boat-racing meeting" , "for crafty rivals" , "Yachting or rowing event" , "Boating event" .)