The most common and most likely answer to this crossword clue is the 8 letter word KNOCKOUT
I've seen this crossword clue in The Guardian
K
N
O
C
K
O
U
T
More clues leading to the result KNOCKOUT
- Blow striking person
- Stunner dismissed after 17
- Result of last punch, a beauty!
- Pilgrimage site not to be considered? Excellent!
- Great innings, then dismissed
- Fabulous way to stop opponent
- Amazing result of strike
- Attractive form of competition
- Final delivery could be outstandingly attractive
- Foreman’s aim, maybe, that’s excellent?
Buddy explains!

The straight part
We know that "Stunner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stunner = knockout.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 KNOCKOUT mean?
KNOCKOUT noun- The act of making someone unconscious, or at least unable to come back on their feet within a certain period of time; a TKO.
- The deactivation of anything.
- Something wildly popular, entertaining, or funny.
- A very attractive person, especially a beautiful woman.
- A partially punched opening meant for optional later removal.
- The deactivation of a particular gene.
- A creature engineered with a particular gene deactivated.
- An event where a foreground color causes a background color not to print.
- A tournament in which a team or player must beat the opponent in order to progress to the next round.
- A simple game for two or more players, derived from basketball.
- A knockout auction.
- Rendering someone unconscious.
- Amazing; gorgeous; beautiful.
- Designating an organism in which a particular gene has been removed or deactivated.
- Causing elimination from a competition