The most common and most likely answer to this crossword clue is the 6 letter word LUNACY
I've seen this crossword clue in The Times
L
U
N
A
C
Y
More clues leading to the result LUNACY
- Loss of marbles from net-like bagging one used in Paris
- Fluky to lose king, capturing a knight back? Madness
- Delicately woven clothing a French folly
- Punk shaved, fancy trousers folly
- Frilly clothing for French individual? That’s madness
- It’s extreme folly for girl to welcome an uprising
- Folly having fancy decoration around international body
- Girl swallowing sodium — it’s madness
- Folly of woman having upsetting article implanted
- Anzac regulars billeted in Miss Locket’s folly
Buddy explains!

The straight part
We know that "Loss of marbles" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case loss of marbles = lunacy.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 LUNACY mean?
LUNACY noun- (of a person or group of people) The state of being mad, insanity
- Something deeply misguided.