The most common and most likely answer to this crossword clue is the 11 letter word SKULDUGGERY
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Buddy explains!

The straight part
We know that "ugly practice" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ugly practice = skulduggery.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 SKULDUGGERY mean?
SKULDUGGERY noun- A devious device or trick.
- Dishonest, underhanded, or unscrupulous activities or behaviour.