Rod's son cheers very loudly (5)
I believe the answer is:
'rod's' is the definition.
(I've seen this in another clue)
'son cheers very loudly' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'cheers' becomes 'ta' (both can informally mean thank you).
'very loudly' becomes 'ff' (short for fortissimo, 'very loud' in music).
(Other definitions for staff that I've seen before include "Walking-stick" , "Rod of authority" , "Employees; rod" , "Employees; weapon" , "Emblem of authority" .)