The most common and most likely answer to this crossword clue is the 4 letter word CHAW
I've seen this crossword clue in Financial Times
C
H
A
W
Buddy explains!
The straight part
We know that "bit of tobacco" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bit of tobacco = chaw.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 CHAW mean?
CHAW noun- Chewing tobacco.
- A plug or wad of chewing tobacco.
- The jaw.
- To chew; to grind with one's teeth; to masticate (food, or the cud)
- To ruminate (about) in thought; to ponder; to consider
- To steal.