It's obvious I'd engaged in contest (7)
I believe the answer is:
evident
'it's obvious' is the definition.
('evident' can be similar in meaning to 'obvious')
'i'd engaged in contest' is the wordplay.
'engaged in' indicates putting letters inside.
'contest' becomes 'event' (I've seen this before).
'id' put within 'event' is 'EVIDENT'.
(Other definitions for evident that I've seen before include "Obvious, may be plainly seen" , "Readily apparent" , "Obvious, quite apparent" , "Clearly apparent" , "Patent" .)