Astound or amaze (4,4)
I believe the answer is:
bowl over
I believe this clue is a double definition.
'astound' is the first definition.
(thesaurus)
'amaze' is the second definition.
(thesaurus)
(Other definitions for bowl over that I've seen before include "Greatly surprise" , "really impress" , "Overwhelm with surprise or emotion - at cricket?" , "Deliver six balls on the cricket pitch" , "Thoroughly delight" .)