The most common and most likely answer to this crossword clue is the 6 plus 2 letter word SQUARE UP
I've seen this crossword clue in The Guardian
S
Q
U
A
R
E
U
P
More clues leading to the result SQUARE UP
- Prepare to scrap pay
- Prepare to fight fuddy-duddy in court
- Prepare for fight … or settle
- Just winning, prepare for a fight
- Settle‘s marketplace perhaps under repair
- Confront someone winning by four, perhaps?
- Get ready to fight in fair at university
- Settle as conventional person at Oxford?
- Settle, or prepare for a fight
- Level, then winning — prepare to fight
Buddy explains!

The straight part
We know that "prepare for a fight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prepare for a fight = square up.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.