Formally admit sport is overcome by greed? (5,2)
I believe the answer is:
swear in
'formally admit' is the definition.
(I've seen this before)
'sport is overcome by greed?' is the wordplay.
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'is overcome by' means one lot of letters goes inside another.
'greed?' becomes 'sin' (greed is a kind of sin).
'wear' inserted inside 'sin' is 'SWEAR IN'.
(Other definitions for swear in that I've seen before include "Admit to office" , "prepare to deliver evidence" , "Administer official oath" , "Inaugurate by oath" , "Formally admit" .)