Obsessive staff in charge (5)
I believe the answer is:
manic
'obsessive' is the definition.
(I've seen this before)
'staff in charge' is the wordplay.
'staff' becomes 'man' (as in staffing or manning a particular place).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'man'+'ic'='MANIC'
(Other definitions for manic that I've seen before include "Showing wild excitement" , "Frenetic, mad" , "Berserk" , "Obsessive" , "On a pathological high" .)