The most common and most likely answer to this crossword clue is the 10 letter word LOCOMOTIVE
I've seen this crossword clue in The Times
L
O
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M
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More clues leading to the result LOCOMOTIVE
- Train driver’s crazy reason for acting
- Rocket, perhaps, old officer sent up with reason
- See firm reason for alternative to car?
- Crazy reason for moving without assistance
- Crazy reason one is found on-line
- See company incentive and train
- Crazy reason for moving from place to place
- Nuts ground in big machine
- Able to move by oneself in order to live around lake
- Vehicle with a screw loose on purpose
Buddy explains!

The straight part
We know that "moving without assistance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moving without assistance = locomotive.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 LOCOMOTIVE mean?
LOCOMOTIVE noun- The power unit of a train that pulls the coaches or wagons.
- A traction engine
- A cheer characterized by a slow beginning and a progressive increase in speed
- A country which drives the world economy by having a high level of imports. (i.e. The United States).
- Of or relating to locomotion
- Of or relating to the power unit of a train which does not carry passengers or freight itself