The most common and most likely answer to this crossword clue is the 5 letter word BADLY
I've seen this crossword clue in The Daily Telegraph
B
A
D
L
Y
Buddy explains!

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 BADLY mean?
BADLY adjective- Ill, unwell.
- In a bad manner.
- Very much; to a great degree.