Outstrip expectations (5)
I believe the answer is:
amaze
'outstrip expectations' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for amaze that I've seen before include "Surprise greatly, astonish" , "Greatly surprise, fill with wonder" , "Cause wonder" , "Flabbergast" , "Confound with wonder" .)