The most common and most likely answer to this crossword clue is the 6 letter word COMBAT
I've seen this crossword clue in The Guardian
C
O
M
B
A
T
More clues leading to the result COMBAT
- Fight Club follows The Big Sleep
- Struggle with marsupial caught for wife
- Firm doctor engaged in battle
- Doctor in cape, fighting
- Fight doctor in film
- Marsupial heading off after end of epic fight
- Doctor dons jacket for action
- Maiden interrupts county cricketer’s fight
- Say World War II search area, tense
- Oppose heartless mob, breaking cover
Buddy explains!

The straight part
We know that "fight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fight = combat.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 COMBAT mean?
COMBAT noun- A battle, a fight (often one in which weapons are used).
- A struggle for victory
- To fight; to struggle against.
- To fight (with); to struggle for victory (against).