The most common and most likely answer to this crossword clue is the 7 letter word BELONGS
I've seen this crossword clue in The Times
B
E
L
O
N
G
S
Buddy explains!

The straight part
We know that "fits" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fits = belongs.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 BELONGS mean?
BELONGS verb- To have its proper place.
- (followed by to) To be part of, or the property of.
- (followed by to) To be the spouse or partner of.
- (followed by to) To be an element of (a set). The symbol \in means belongs to.
- To be deserved by.