Talk about endless event (6)
I believe the answer is:
discus
'event' is the definition.
(athletics event)
'talk about endless' is the wordplay.
'talk about' becomes 'discuss' (to discuss something is to talk about it).
'endless' means to remove the last letter.
'discuss' with its final letter taken off is 'DISCUS'.
(Other definitions for discus that I've seen before include "Object thrown by athletes" , "Athlete's projectile" , "Field event projectile" , "Circular object thrown in sports" , "Field sport" .)