Surprise by getting the old right in! (7)
I believe the answer is:
startle
'surprise' is the definition.
(to startle someone is to surprise or shock them)
'getting the old right in' is the wordplay.
'getting' is an insertion indicator.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'old' becomes 'stale' (associated in meaning).
'right' becomes 'r' (abbreviation).
'in' means one lot of letters goes inside another.
't' placed inside 'stale' is 'statle'.
'statle' enclosing 'r' is 'STARTLE'.
'by' acts as a link.
(Other definitions for startle that I've seen before include "Astonish" , "Rattles (anag.)" , "Surprise with starlet" , "Cause shock to" , "Make jump" .)