The most common and most likely answer to this crossword clue is the 7 letter word VICTOR*
I've seen this crossword clue in The Guardian
V
I
C
T
O
R
*
Buddy explains!
The straight part
We know that "Champion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case champion = victor*.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 VICTOR* mean?
VICTOR* noun- The winner in a fight or contest.
- The letter V in the ICAO spelling alphabet.