The most common and most likely answer to this crossword clue is the 10 letter word DECATHLETE
I've seen this crossword clue in The Times
D
E
C
A
T
H
L
E
T
E
More clues leading to the result DECATHLETE
- Competitor felt cheated somehow, first to be eliminated
- Olympian cheated when swimming without permit
- All-round competitor having cheated, let off
- Strike involving Catholic all-rounder on track
- Competitor cheated dreadfully, having got let in
- Unusual chat going into function of key versatile competitor
- Versatile sportsman allowed to enter cheated appallingly
Buddy explains!

The straight part
We know that "Competitor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case competitor = decathlete.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 DECATHLETE mean?
DECATHLETE noun- An athlete who competes in the decathlon.