The most common and most likely answer to this crossword clue is the 8 letter word SPONSORS
I've seen this crossword clue in The Daily Telegraph
S
P
O
N
S
O
R
S
Buddy explains!

The straight part
We know that "Supporters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supporters = sponsors.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 SPONSORS mean?
SPONSORS noun- A person or organisation with some sort of responsibility for another person or organisation, especially where the responsibility has a religious, legal, or financial aspect.
- One that pays all or part of the cost of an event, a publication, or a media program, usually in exchange for advertising time.
- To be a sponsor for.