Cries, upsetting the boss (4)
I believe the answer is:
sobs
'cries' is the definition.
(sobbing is a kind of crying)
'upsetting the boss' is the wordplay.
'upsetting' indicates anagramming the letters.
'boss' anagrammed gives 'SOBS'.
(Other definitions for sobs that I've seen before include "Weeps heavily for boss" , "Cries loudly" , "Weeps heavily (4)" , "Weeps noisily" , "cries uncontrollably" .)