The most common and most likely answer to this crossword clue is the 7 letter word RUNOFFS
I've seen this crossword clue in The Times
R
U
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O
F
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Buddy explains!
The straight part
We know that "deciding contests" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case deciding contests = runoffs.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 RUNOFFS mean?
RUNOFFS noun- That portion of precipitation or irrigation on an area which does not infiltrate or evaporate, but instead is discharged from the area.
- Dissolved chemicals, etc, included in such water.
- A second or further round of an indecisive election, after other candidates (often all but the last two) have been eliminated.