The most common and most likely answer to this crossword clue is the 8 letter word TRIALIST
I've seen this crossword clue in The Times
T
R
I
A
L
I
S
T
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 = trialist.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 TRIALIST mean?
TRIALIST noun- An advocate of trialism, especially with reference to the proposed creation of a state comprising Austria, Hungary, and a Slavic region.
- Involving three elements; especially, pertaining to a potential state comprising Austria, Hungary, and a Slavic region.
- A person who takes part in a trial (of a drug etc.)