Some prize stimulates enthusiasm (4)
I believe the answer is:
zest
'enthusiasm' is the definition.
(zest can mean enthusiasm or eagerness)
'some prize stimulates' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ZEST' can be found hidden inside 'prize stimulates'.
(Other definitions for zest that I've seen before include "Outer layer of citrus peel" , "Enthusiasm - grated lemon peel" , "Piquancy - fruit rind" , "Piquancy (eg from lemon peel)" , "Vigour" .)