The most common and most likely answer to this crossword clue is the 4 plus 1 plus 5 plus 5 letter word HAVE A SCREW LOOSE
I've seen this crossword clue in The Daily Telegraph
H
A
V
E
A
S
C
R
E
W
L
O
O
S
E
More clues leading to the result HAVE A SCREW LOOSE
- Be unbalanced as cow almost leaves horse rattled
- Serve aloo with cashew nuts? You have to be crazy!
- Be crazy in hold when sailors get relaxed
- Be a bit mad, having lost the thread?
- Be slightly unbalanced and resolve a case — how unorthodox
- Be out to lunch and partake of a singular set of facilities in NW town
- Rampaging roaches leave sow cuckoo
- Crazy how ace resolves a problem
Buddy explains!
The straight part
We know that "Be slightly unbalanced" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case be slightly unbalanced = have a screw loose.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.