Eccentric ace gets trophy (8)
I believe the answer is:
crackpot
'eccentric' is the definition.
(I know that crackpot is a type of eccentric)
'ace gets trophy' is the wordplay.
'ace' becomes 'crack' (I've seen this before).
'gets' means one lot of letters go next to another.
'trophy' becomes 'pot' (type of trophy).
'crack'+'pot'='CRACKPOT'
(Other definitions for crackpot that I've seen before include "Fruitcake, screwball" , "Idiot" , "Foolish" , "crazy type" , "Crazy or impractical person" .)