Flat season without maiden horse (7)
I believe the answer is:
eventer
'horse' is the definition.
(horse competing in equestrian events)
'flat season without maiden' is the wordplay.
I cannot really see how this works, but
'flat' could be 'even' (level) and 'even' is found in the answer.
The remaining letters 'ter' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eventer that I've seen before include "competitive horse" , "versatile horse" , "Showjumper" , "Equestrian horse" , "Sportsman" .)