Argue about being second-placed in field event (7)
I believe the answer is:
discuss
'argue' is the definition.
(discussing is a kind of arguing)
'being second-placed in field event' is the wordplay.
'being second' becomes 's' (common abbreviation).
'placed in' is an insertion indicator (I've seen this in other clues).
'field event' becomes 'discus' (discus is a kind of field event).
's' going into 'discus' is 'DISCUSS'.
'about' acts as a link.
(Other definitions for discuss that I've seen before include "Settle" , "Go into" , "Debate" , "Take up" , "Consider" .)