The most common and most likely answer to this crossword clue is the 8 letter word CAPTURED
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Buddy explains!

The straight part
We know that "in the bag" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in the bag = captured.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 CAPTURED mean?
CAPTURED verb- To take control of; to seize by force or stratagem.
- To store (as in sounds or image) for later revisitation.
- To reproduce convincingly.
- To remove or take control of an opponent’s piece in a game (e.g., chess, go, checkers).