Bachelor originally attending tennis club (3)
I believe the answer is:
bat
'club' is the definition.
(bat is a kind of club)
'bachelor originally attending tennis' is the wordplay.
'bachelor' becomes 'b' (abbreviation e.g. BA=Bachelor of Arts).
'originally' indicates taking the first letters.
The first letters of 'attending tennis' is 'at'.
'b'+'at'='BAT'
(Other definitions for bat that I've seen before include "Night flier" , "Nocturnal mouselike mammal" , "Nocturnal flier" , "Pipistrelle" , "once wielded by 60 [GREIG]" .)