The most common and most likely answer to this crossword clue is the 4 letter word TOSA
T
O
S
A
More clues leading to the result TOSA
Buddy explains!
The straight part
We know that "Fighting dog" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fighting dog = tosa.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 TOSA mean?
TOSA noun- A Japanese breed of fighting dog