Mark has excellent staff (4)
I believe the answer is:
mace
'staff' is the definition.
(a mace is a ceremonial staff or stick)
'mark has excellent' is the wordplay.
'mark' becomes 'm'.
'has' is a charade indicator (letters next to each other).
'excellent' becomes 'ace' (ace can informally mean very good).
'm'+'ace'='MACE'
(Other definitions for mace that I've seen before include "Spice; ceremonial baton" , "Came to find ceremonial staff" , "Came to get ceremonial staff" , "Came to get ancient weapon" , "Staff - ground nutmeg" .)