Leader sobs when upset (4)
I believe the answer is:
boss
'leader' is the definition.
(boss is a kind of leader)
'sobs when upset' is the wordplay.
'when upset' indicates anagramming the letters.
'sobs' with letters rearranged gives 'BOSS'.
(Other definitions for boss that I've seen before include "Bully" , "Behave overbearingly" , "Stud; chief" , "Leader; stud" , "Team manager" .)