The most common and most likely answer to this crossword clue is the 12 letter word CHEERLEADERS
I've seen this crossword clue in The Times
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More clues leading to the result CHEERLEADERS
Buddy explains!
The straight part
We know that "Vocal supporters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vocal supporters = cheerleaders.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 CHEERLEADERS mean?
CHEERLEADERS noun- A person, usually a young, attractive female, who encourages applause and cheers at a sports event, and wearing a specially-designed uniform in the official colors of the team he/she cheers for.
- A person who rallies support for any cause.