One in five going on foot (3)
I believe the answer is:
toe
'foot' is the definition.
(toeing is a kind of footing)
'one in five going' is the wordplay.
'one' becomes 'o' (I've seen this in other clues).
'in' indicates putting letters inside.
'five going' becomes 'te' (I can't explain this - if you can you should believe this answer much more).
'o' going into 'te' is 'TOE'.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for toe that I've seen before include "Drive obliquely" , "Lower digit" , "Feature of footwear" , "Digit on foot" , "One of the lower digits" .)