Bowl over during Test, unsuccessfully (4)
I believe the answer is:
stun
'bowl over' is the definition.
(I've seen this before)
'during test unsuccessfully' is the wordplay.
'during' indicates a hidden word.
'STUN' is hidden within 'test unsuccessfully'.
(Other definitions for stun that I've seen before include "Surprise greatly or daze" , "Daze with nuts" , "Leave speechless" , "Render semi-conscious with blow" , "Shock or astonish" .)