Debate holding the field event on Sunday (7)
I believe the answer is:
discuss
'debate' is the definition.
(to discuss something is to debate it)
'the field event on sunday' is the wordplay.
'the field event' becomes 'discus' (discus is a kind of field event).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'sunday' becomes 's'.
'discus'+'s'='DISCUSS'
'holding' acts as a link.
(Other definitions for discuss that I've seen before include "Argue" , "Go into" , "Verbally T [TREAT]" , "Take up" , "Confer" .)