The most common and most likely answer to this crossword clue is the 7 letter word SHATTER
I've seen this crossword clue in The Times
S
H
A
T
T
E
R
More clues leading to the result SHATTER
- One attending tea party after small break
- Ruin brought by second mad person
- Son and cap-maker suddenly go to pieces
- Deeply disturb small milliner
- Scaffolder at top, one making tiles break
- Surprise Mum with an unusual treat
- Greatly upset Southern tile supplier
- Ruin created by little son, mad fellow?
- Dash to pieces with wild threats
- Second mad person having tea break
Buddy explains!

The straight part
We know that "Ruin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ruin = shatter.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 SHATTER mean?
SHATTER noun- A fragment of anything shattered.
- A (pine) needle.
- A form of concentrated cannabis.
- To violently break something into pieces.
- To destroy or disable something.
- To smash, or break into tiny pieces.
- To dispirit or emotionally defeat
- To scatter about.