Stocking only occasionally goes over large leg (5)
I believe the answer is:
nylon
'stocking' is the definition.
(nylon stocking is a kind of stocking)
'only occasionally goes over large leg' is the wordplay.
'occasionally' means one should take alternating letters.
'goes over large' becomes 'l' (I can't explain this - if you can you should believe this answer much more).
'leg' becomes 'on' (cricket term, fielding positions).
The alternating letters of 'only' are 'ny'.
'ny'+'l'+'on'='NYLON'
Can you help me to learn more?
(Other definitions for nylon that I've seen before include "Man-made fibre" , "Cover for leg" , "may be damaged by running" , "The first synthetic fibre" , "Artificial cloth" .)