The most common and most likely answer to this crossword clue is the 10 letter word STANCHIONS
I've seen this crossword clue in The Daily Telegraph
S
T
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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 = stanchions.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 STANCHIONS mean?
STANCHIONS noun- A vertical pole, post, or support.
- A framework of such posts, used to secure or confine cattle.
- To erect stanchions, or equip something with stanchions.
- To confine by means of stanchions, typically used for cattle.