The most common and most likely answer to this crossword clue is the 3 letter word TAW
I've seen this crossword clue in The Daily Telegraph
T
A
W
More clues leading to the result TAW
Buddy explains!

The straight part
We know that "Marble" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marble = taw.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 TAW mean?
TAW noun- Tawed leather.
- To prepare or dress, as hemp, by beating; to tew.
- (by extension) To beat; to scourge.
- To dress and prepare, as the skins of sheep, lambs, goats, and kids, for gloves, etc., by imbuing them with alum, salt, and other agents, for softening and bleaching them.
- A favorite marble in the game of marbles.
- A line or mark from which the players begin a game of marbles.
- (square dancing) A dance partner.
- A favorite person; beloved, partner, spouse.
- To shoot a marble.
- The 22nd and last letter of many Semitic alphabets/abjads, including Phoenician, Aramaic, Hebrew, Syriac and Arabic.
- To push; to tug; to tow.