Hospital excluded from surprise strike (4)
I believe the answer is:
sock
'strike' is the definition.
(I've seen this before)
'hospital excluded from surprise' is the wordplay.
'hospital' becomes 'h'.
'excluded from' indicates named letters should be taken away.
'surprise' becomes 'shock' (shock is a kind of surprise).
'shock' with 'h' removed is 'SOCK'.
(Other definitions for sock that I've seen before include "Hit; horse's leg marking" , "Thump" , "one with wind" , "impact" , "Item of clothing" .)