One may replace Yale lecturer with hick, most foolishly (9)
I believe the answer is:
locksmith
'one may replace yale' is the definition.
(Yale is a type of lock)
'lecturer with hick most foolishly' is the wordplay.
'lecturer' becomes 'l' (abbreviation for lecturer).
'with' says to put letters next to each other.
'foolishly' indicates an anagram.
'hick'+'most'='hickmost'
'hickmost' with letters rearranged gives 'ocksmith'.
'l'+'ocksmith'='LOCKSMITH'
(Other definitions for locksmith that I've seen before include "Yale scholar" , "key figure" , "laughing stock" , "Maker of secure fasteners" , "Maker of security devices" .)