Beast pins hero in crucial contest (7)
I believe the answer is:
decider
'crucial contest' is the definition.
The definition suggests a singular noun which matches the answer.
'beast pins hero in' is the wordplay.
'beast pins' becomes 'deer' (I can't explain this - if you can you should believe this answer much more).
'hero' becomes 'Cid' (El Cid, Spanish military hero).
'in' is an insertion indicator.
'deer' placed around 'cid' is 'DECIDER'.
Can you help me to learn more?
(Other definitions for decider that I've seen before include "Settler" , "important game" , "Ultimate goal" , "Replay perhaps" , "It produces a winner after a drawn series" .)
