Endlessly talk about field event (6)
I believe the answer is:
discus
'field event' is the definition.
(discus is a kind of field event)
'endlessly talk about' is the wordplay.
'endlessly' means to remove the last letter.
'talk about' becomes 'discuss' (to discuss something is to talk about it).
'discuss' with its last letter removed is 'DISCUS'.
(Other definitions for discus that I've seen before include "Object thrown by athletes" , "Olympic throwing event" , "Something thrown by athletes" , "sports equipment" , "Object thrown in field sports" .)