Open race I had entered (7)
I believe the answer is:
evident
'open' is the definition.
(thesaurus)
'race i had entered' is the wordplay.
'race' becomes 'event' (I've seen this before).
'i had' becomes 'id' (I'd).
'entered' means one lot of letters goes inside another.
'event' going around 'id' is 'EVIDENT'.
(Other definitions for evident that I've seen before include "Readily apparent" , "Plain, obvious, clear" , "Plain to see" , "Comprehensible - manifest" , "Noticeable" .)