Walked first of the staff to study (7)
I believe the answer is:
trodden
'walked' is the definition.
(I've seen this before)
'first of the staff to study' is the wordplay.
'first of the' becomes 't' (1st letter of 'the').
'staff' becomes 'rod' (both can mean a stick or cane).
'to study' becomes 'den' (den can mean an office or study).
't'+'rod'+'den'='TRODDEN'
(Other definitions for trodden that I've seen before include "Oppressed" , "Crushed underfoot" , "Footpaths are" , "Stepped on" , "Trampled" .)