The most common and most likely answer to this crossword clue is the 8 letter word CLAIMANT
I've seen this crossword clue in The Guardian
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More clues leading to the result CLAIMANT
- I must interrupt noisy petitioner
- One hoping for beneficial response, say, lacks the power to secure mail operative
- One bringing law suit, wild animal in court
- He goes to court to demand a social worker
- Calling urgently about one petitioner
- Excellent fellow pursuing line in court — one looking for compensation?
- Petitioner, one inside demanding attention
- One inhibited by noisy petitioner
- Legal petitioner‘s humbug, left with ambition squashed
- He demands list containing sorted mail
Buddy explains!

The straight part
We know that "One hoping for beneficial response, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one hoping for beneficial response, say = claimant.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 CLAIMANT mean?
CLAIMANT noun- One who claims; one who makes a claim.
- A person receiving money from the government, in a form of unemployment benefits, disability benefits or similar.
- The party who initiates a lawsuit before a court.