Sport needing a hundred in syndicate (6)
I believe the answer is:
racing
'sport' is the definition.
(racing is a kind of sport)
'a hundred in syndicate' is the wordplay.
'hundred' becomes 'c' (Roman numeral).
'in' indicates putting letters inside.
'syndicate' becomes 'ring' (I've seen this in other clues).
'a'+'c'='ac'
'ac' placed within 'ring' is 'RACING'.
'needing' acts as a link.
(Other definitions for racing that I've seen before include "Epsom, Aintree sport" , "operating at great speed" , "Speed sport" , "going very fast" , "Dashing" .)