The most common and most likely answer to this crossword clue is the 6 letter word FIDGET
I've seen this crossword clue in The Guardian
F
I
D
G
E
T
More clues leading to the result FIDGET
- Restless type able to swallow date, say, upside down
- Right out of the cooler, thief’s beginning to show unease
- Down
- Show agitation as little one undergoes sex change
- Move restlessly following identification and capture
- Perhaps gifted young scholars may be told not to
- Well bored by Democratrambling, you may do this
- Scarce gifted, I twitch body, leg or arm
- Dog dropped tail to receive fuss
- Shuffle folio papers and secure
Buddy explains!

The straight part
We know that "I twitch body, leg or arm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i twitch body, leg or arm = fidget.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 FIDGET mean?
FIDGET noun- A nervous wriggling or twitching motion.
- A person who fidgets, especially habitually.
- A toy intended to be fidgeted with.
- To wiggle or twitch; to move around nervously or idly.
- To cause to fidget; to make uneasy.