The most common and most likely answer to this crossword clue is the 8 letter word MATADORS
I've seen this crossword clue in The Daily Telegraph
M
A
T
A
D
O
R
S
Buddy explains!

The straight part
We know that "men fighting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case men fighting = matadors.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 MATADORS mean?
MATADORS noun- The person whose aim is to kill the bull in a bullfight.
- A certain game of dominoes in which four dominoes (the 4-3, 5-2, 6-1, and double blank), called matadors, may be played at any time in any way.
- The jack of clubs, or any other trump held in sequence with it, in the game of skat.
- One of the three chief cards in ombre and quadrille.