Sports chiefs tucking into endless snacks and some sort of pudding (7)
I believe the answer is:
tapioca
'some sort of pudding' is the definition.
(type of pudding)
'sports chiefs tucking into endless snacks' is the wordplay.
'sports chiefs' becomes 'IOC' (International Olympic Committee).
'tucking into' means one lot of letters goes inside another.
'endless' means to remove the last letter.
'snacks' becomes 'tapas' (type of Spanish snack).
'tapas' with its final letter removed is 'tapa'.
'ioc' placed within 'tapa' is 'TAPIOCA'.
'and' acts as a link.
(Other definitions for tapioca that I've seen before include "course" , "Starchy pudding" , "Pudding from the cassava root" , "Hard white cassava grains used for puddings" , "Foodstuff used as a thickener" .)