The most common and most likely answer to this crossword clue is the 6 letter word TOGGLE
I've seen this crossword clue in The Guardian
T
O
G
G
L
E
More clues leading to the result TOGGLE
- Switch between two positions, as leg got twisted
- Button had returned with broken leg
- Change function of button
- Peg leg got broken
- Kick clothes horse, having lost fastener
- Switch to goods connected with the French
- Leg got twisted in crosspiece
- Leg got broken in little bar
- Fastener caught up on broken leg
- Piggy banks good girl emptied for change?
Buddy explains!

The straight part
We know that "crosspiece" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crosspiece = toggle.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 TOGGLE mean?
TOGGLE noun- A wooden or metal pin, short rod, crosspiece or similar, fixed transversely in the eye of a rope or chain to be secured to any other loop, ring, or bight, e.g. a sea painter to a lifeboat.
- (in particular) A rod-shaped button bound with slack to the fabric.
- A toggle switch.
- An appliance for transmitting force at right angles to its direction.
- A horizontal piece of wood that is placed on a door, flat, or other wooden structure, but is not on one of the edges of the structure.
- (skydiving) A loop of webbing or a dowel affixed to the end of the steering/brake lines of a parachute providing the pilot with a means of control.
- To alternate between two positions using a single switch or lever.
- To switch between alternate states.
- To fix like a toggle iron; to fix fast.