Surprise the French after kick-off (7)
I believe the answer is:
'surprise' is the definition.
(to startle someone is to surprise or shock them)
'the french after kick-off' is the wordplay.
'the french' becomes 'le' ('the' in French).
'after' says to put letters next to each other.
'kick off' becomes 'start' (start of a football match).
'le' put after 'start' is 'STARTLE'.
(Other definitions for startle that I've seen before include "Surprise with starlet" , "Alarm suddenly" , "Take by surprise" , "Rattles (anag.)" , "Astonish" .)