The most common and most likely answer to this crossword clue is the 6 letter word BLENCH
I've seen this crossword clue in Independent
B
L
E
N
C
H
More clues leading to the result BLENCH
Buddy explains!

The straight part
We know that "Make sudden move" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case make sudden move = blench.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BLENCH mean?
BLENCH noun- A deceit; a trick.
- A sidelong glance.
- To shrink; start back; give way; flinch; turn aside or fly off.
- (of the eye) To quail.
- To deceive; cheat.
- To draw back from; shrink; avoid; elude; deny, as from fear.
- To hinder; obstruct; disconcert; foil.
- To fly off; to turn aside.
- To blanch.