The most common and most likely answer to this crossword clue is the 10 letter word OVERTURNED
I've seen this crossword clue in The Sunday Telegraph
O
V
E
R
T
U
R
N
E
D
Buddy explains!

The straight part
We know that "capsized" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case capsized = overturned.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 OVERTURNED mean?
OVERTURNED verb- To turn over, capsize or upset.
- To overthrow or destroy.
- To reverse (a decision); to overrule or rescind.
- To diminish the significance of a previous defeat by winning; to make a comeback from.