The most common and most likely answer to this crossword clue is the 8 letter word CHAMPION
I've seen this crossword clue in The Times
C
H
A
M
P
I
O
N
More clues leading to the result CHAMPION
- Back from church with claim to devotion -- touching!
- Winner such as Bob at Aintree in 1981? . . . .
- Penny sporting dreadful Mohican, or a number one?
- [Guardian group accepts position of Corbyn, Opposition leader]
- Gold medallist is back
- Horticulturalist initially cutting plant back
- Best solver embodying Holmes, initially
- Top-notch detective capturing hearts
- Support excellent hero
- Guard for flower hot housed
Buddy explains!

The straight part
We know that "Back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case back = champion.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 CHAMPION mean?
CHAMPION noun- An ongoing winner in a game or contest.
- Someone who is chosen to represent a group of people in a contest.
- Someone who fights for a cause or status.
- Someone who fights on another's behalf.
- To promote, advocate, or act as a champion for (a cause, etc.).
- To challenge.
- Acting as a champion; that has defeated all one's competitors.
- Excellent; beyond compare.
- (predicative) Excellent; brilliant; superb; deserving of high praise.