The most common and most likely answer to this crossword clue is the 4 plus 3 letter word WORN OUT
I've seen this crossword clue in The Guardian
W
O
R
N
O
U
T
Buddy explains!
The straight part
We know that "All in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case all in = worn out.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 WORN OUT mean?
WORN OUT adjective- Damaged due to hard or continued use or exposure until no longer useful or effective.
- Exhausted or fatigued from exertion.