The most common and most likely answer to this crossword clue is the 7 letter word PLAYOFF
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Buddy explains!

The straight part
We know that "extra game" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extra game = playoff.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 PLAYOFF mean?
PLAYOFF noun- A final game in a series needed to break a tie.
- A short series of games to select a league champion.