The most common and most likely answer to this crossword clue is the 9 letter word SUPPLIANT
I've seen this crossword clue in The Guardian
S
U
P
P
L
I
A
N
T
More clues leading to the result SUPPLIANT
Buddy explains!

The straight part
We know that "begging" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case begging = suppliant.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 SUPPLIANT mean?
SUPPLIANT noun- One who pleads or requests earnestly.
- Entreating with humility.
- Supplying; auxiliary.