The most common and most likely answer to this crossword clue is the 5 letter word BOOBS
I've seen this crossword clue in The Daily Telegraph
B
O
O
B
S
Buddy explains!

The straight part
We know that "drops the ball" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drops the ball = boobs.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 BOOBS mean?
BOOBS noun- Idiot, fool.
- To behave stupidly; to act like a boob.
- To make a mistake
- A breast, especially that of an adult or adolescent human female.
- A prison; jail.