Write quickly about large surprise (4)
I believe the answer is:
jolt
'surprise' is the definition.
(I've seen this in another clue)
'write quickly about large' is the wordplay.
'write quickly' becomes 'jot' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'large' becomes 'L' (eg in clothes sizes).
'jot' placed around 'l' is 'JOLT'.
(Other definitions for jolt that I've seen before include "Sudden impact" , "Sudden jerk" , "Sudden shock" , "Jostle; shock" , "Knock sharply so as to dislodge" .)