Unfortunate case of Hindu ascetic begging alms (5)
I believe the answer is:
'ascetic begging alms' is the definition.
(term for an Indian ascetic)
'unfortunate case of hindu' is the wordplay.
'unfortunate' becomes 'sad' (I've seen this before).
'case of' says to hollow out the word (remove centre letters) (outsides of).
'hindu' with its centre removed is 'hu'.
(Other definitions for sadhu that I've seen before include "Indian wandering holy man" , "Hindu wandering holy man" , "Ascetic" , "one choosing austerity" , "Indian holy man or sage" .)