The most common and most likely answer to this crossword clue is the 10 letter word CONTESTANT
I've seen this crossword clue in The Sunday Telegraph
C
O
N
T
E
S
T
A
N
T
More clues leading to the result CONTESTANT
- Surprisingly cast net, not being a competitor
- Happy to include singular terriers as competition entry
- Competitor cannot broadcast about match
- Rival to study before exam — an exemplary worker
- Happy to embrace good person, a competitor
- He struggles to study before exam — exemplary worker
- One of those competing in uniform, including half of team
- One taking part in match between two opponents
- Match being held inside cannot upset competitor
- Rival happy to describe detailed attempt
Buddy explains!

The straight part
We know that "One of those competing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of those competing = contestant.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 CONTESTANT mean?
CONTESTANT noun- A participant in a contest; specifically, a person who plays a game, as on a TV game show.
- One who brings a legal challenge.