I had to enter competition, it's clear (7)
I believe the answer is:
evident
'clear' is the definition.
('evident' can be a synonym of 'clear')
'i had to enter competition' is the wordplay.
'i had' becomes 'id' (I'd).
'to enter' means one lot of letters goes inside another.
'competition' becomes 'event' (I've seen this before).
'id' put inside 'event' is 'EVIDENT'.
'it's' acts as a link.
(Other definitions for evident that I've seen before include "clearly visible" , "Quite obvious, easy to see" , "Clearly apparent" , "Obvious - 1 across" , "Obvious, quite apparent" .)