The most common and most likely answer to this crossword clue is the 10 letter word SUPPORTING
I've seen this crossword clue in The Sunday Telegraph
S
U
P
P
O
R
T
I
N
G
Buddy explains!

The straight part
We know that "pro" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pro = supporting.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.
Crossword Answer definitions
SUPPORTING verb- To keep from falling.
- To answer questions and resolve problems regarding something sold.
- To back a cause, party, etc., mentally or with concrete aid.
- To help, particularly financially.
- To verify; to make good; to substantiate; to establish; to sustain.
- To serve, as in a customer-oriented mindset; to give support to.
- To be designed (said of machinery, electronics, or computers, or their parts, accessories, peripherals, or programming) to function compatibly with or provide the capacity for.
- To be accountable for, or involved with, but not responsible for.
- To endure without being overcome; bear; undergo; to tolerate.
- To assume and carry successfully, as the part of an actor; to represent or act; to sustain.
- That which supports something else; a support.
- That supports.