The most common and most likely answer to this crossword clue is the 7 letter word CAPSIZE
I've seen this crossword clue in The Daily Telegraph
C
A
P
S
I
Z
E
More clues leading to the result CAPSIZE
- Upset milliner might take this off new Lion
- Upset with what one needs to know when buying headgear
- How big top is making you upset
- Flip over how big an accessory is?
- Number in the hat shop creating upset
- Trump measure creates upset
- Turn over important information about prospective international cricketer?
- Turn over hat dimensions
- Turn over detail of school uniform that gives head fit
- Upset, head will have a fit if this is right!
Buddy explains!

The straight part
We know that "upset" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case upset = capsize.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 CAPSIZE mean?
CAPSIZE verb- To overturn.
- To cause (a ship) to overturn.
- (of knots) To deform under stress.