Let off the lead beforehand, which does surprise you (7)
I believe the answer is:
startle
'let off the lead beforehand which does surprise you' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'let off the lead beforehand' is the wordplay.
'off' suggests deleting specific letters ('off' can mean to remove).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'lead' becomes 'start' (I've seen this before).
'beforehand' means one lot of letters go next to another.
'let' with 't' taken out is 'le'.
'le' put after 'start' is 'STARTLE'.
Can you help me to learn more?
(Other definitions for startle that I've seen before include "Cause shock/alarm" , "Cause to feel sudden alarm" , "Make jump" , "Surprise with starlet" , "Take (someone) aback" .)