Eager trainee losing end of decider on points (7)
I believe the answer is:
intense
'eager' is the definition.
(thesaurus)
'trainee losing end of decider on points' is the wordplay.
I cannot quite see how this works, but
'points' could be 'se' and 'se' is located in the answer.
This explanation may well be incorrect...
(Other definitions for intense that I've seen before include "Concentrated, serious" , "say, description of campers?" , "Fierce - deep" , "Of extreme force" , "Extreme - strong" .)