The most common and most likely answer to this crossword clue is the 9 plus 9 letter word GAME, SET AND MATCH
I've seen this crossword clue in The Guardian
G
A
M
E
,
Â
S
E
T
A
N
D
Â
M
A
T
C
H
Buddy explains!
The straight part
We know that "finish on court" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case finish on court = game, set and match.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.