The most common and most likely answer to this crossword clue is the 6 letter word IRRUPT
I've seen this crossword clue in The Daily Telegraph
I
R
R
U
P
T
More clues leading to the result IRRUPT
- Break in congress muffled whirling hum of happiness …
- Burst in as one bishop getting put out
- Italian carrying back sound content to inflict an invasion
- Break into rising contented sound during hanky-panky
- Single sound from a cat coming up, cat finally burst in
- Break in Irish game, point behind
- Break in — sound pleased about it outside
- Break in Ireland game, both sides to profit
- Break, in sound of pleasure from the bottom during sex
- 4 Break in, interrupt forcibly and release ten somehow
Buddy explains!

The straight part
We know that "Break in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case break in = irrupt.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 IRRUPT mean?
IRRUPT verb- To break into.
- To enter forcibly or uninvited.
- To rapidly increase or intensify.