The most common and most likely answer to this crossword clue is the 8 letter word BREAKAGE
I've seen this crossword clue in Financial Times
B
R
E
A
K
A
G
E
More clues leading to the result BREAKAGE
Buddy explains!
The straight part
We know that "Casualty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case casualty = breakage.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 BREAKAGE mean?
BREAKAGE noun- The act of breaking.
- Something that has been broken.
- A service which is unused by a customer, such as an unredeemed gift card, which therefore represents a pure profit to the seller.
- The left-over money in a parimutuel betting pool resulting from rounding off the payoffs, added to the pool for the next race or event or kept as profit.