Foolish people pass out (4)
I believe the answer is:
saps
'foolish people' is the definition.
'pass out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'pass' with letters rearranged gives 'SAPS'.
(Other definitions for saps that I've seen before include "Weakens, undermines" , "Vital juices" , "Weakens, deprives of energy" , "mugs" , "More than one fool" .)