The most common and most likely answer to this crossword clue is the 6 letter word GATING
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More clues leading to the result GATING
Buddy explains!

The straight part
We know that "punishment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case punishment = gating.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 GATING mean?
GATING verb- To keep something inside by means of a closed gate.
- To punish, especially a child or teenager, by not allowing them to go out.
- To open a closed ion channel.
- To furnish with a gate.
- To turn (an image intensifier) on and off selectively as needed, or to avoid damage. See autogating.
- An arrangement of gates.