Pharmacist rides off around enclosures (9)
I believe the answer is:
dispenser
'pharmacist' is the definition.
(I've seen this before)
'rides off around enclosures' is the wordplay.
'off' indicates an anagram.
'around' indicates putting letters inside.
'enclosures' becomes 'pens' (pen is a kind of enclosure).
'rides' anagrammed gives 'diser'.
'diser' enclosing 'pens' is 'DISPENSER'.
(Other definitions for dispenser that I've seen before include "One filling prescription" , "one to give out" , "Pharmacist" , "Container releasing its contents in prescribed amounts" , "Chemist" .)