Field event record set by American (6)
I believe the answer is:
discus
'field event' is the definition.
(discus is a kind of field event)
'record set by american' is the wordplay.
'record' becomes 'disc' (eg a CD, compact disc).
'set by' means one lot of letters go next to another.
'american' becomes 'us' (abbreviation for United States).
'disc'+'us'='DISCUS'
(Other definitions for discus that I've seen before include "flat missile" , "missile launched" , "sports equipment" , "Debate" , "Olympic throwing event" .)