Be in charge of stud (4)
I believe the answer is:
boss
This clue is a double definition.
'be in charge' is the first definition.
(thesaurus)
'stud' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for boss that I've seen before include "Stud; employer" , "Stud; chief" , "Person managing" , "27 [CHIEF]" , "Leader; stud" .)