The most common and most likely answer to this crossword clue is the 4 letter word RUCK
I've seen this crossword clue in The Times
R
U
C
K
More clues leading to the result RUCK
Buddy explains!

The straight part
We know that "Crumple" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crumple = ruck.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 RUCK mean?
RUCK noun- A throng or crowd of people or things; a mass, a pack.
- In Australian rules football
- The situation formed when a player carrying the ball is brought to the ground and one or more members of each side are engaged above the ball, trying to win possession of it; a loose scrum.
- The common mass of people or things; the ordinary ranks.
- To act as a ruck in a stoppage in Australian rules football.
- To contest the possession of the ball in a ruck.
- A crease, a wrinkle, a pucker, as on fabric.
- To crease or fold.
- To become folded.
- To cower or huddle together; to squat; to sit, as a hen on eggs.
- An enormous mythical bird in Eastern legend.
- Rocuronium.
- A rucksack; a large backpack.
- To carry a backpack while hiking or marching.
- A small heifer.