The most common and most likely answer to this crossword clue is the 7 plus 8 letter word SHOTGUN MARRIAGE
I've seen this crossword clue in Financial Times
S
H
O
T
G
U
N
M
A
R
R
I
A
G
E
Buddy explains!
The straight part
We know that "One’s expecting to be in this match maybe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one’s expecting to be in this match maybe = shotgun marriage.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.