Rider given a flat half of bitter (in sport) (7)
I believe the answer is:
eventer
'rider' is the definition.
(I have seen 'Competitive rider ' mean 'eventer' so perhaps 'rider' could also mean 'eventer')
'given a flat half of bitter in sport' is the wordplay.
'given' says to put letters next to each other.
'a flat' becomes 'even' (level).
'half of bitter in sport' becomes 'ter' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'even'+'ter' is 'EVENTER'.
Can you help me to learn more?
(Other definitions for eventer that I've seen before include "Showjumper" , "versatile horse" , "Rider in contests" , "Competing horse or rider" , "Sportsman" .)