Endlessly evaluate fools (5)
I believe the answer is:
asses
'fools' is the definition.
(ass is a kind of fool)
'endlessly evaluate' is the wordplay.
'endlessly' means to remove the last letter.
'evaluate' becomes 'assess' ('assess' can be a synonym of 'evaluate').
'assess' with its last letter removed is 'ASSES'.
(Other definitions for asses that I've seen before include "not the most sensible types" , "Small, sure-footed animals" , "Braying animals" , "More than one fool" , "Animals of horse family" .)