One going on foot, usually with a mate (7)
I believe the answer is:
sneaker
'one going' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'foot usually with a mate' is the wordplay.
I cannot really understand how this works, but
'foot' could be 'sneak' (sneaking is a kind of footing) and 'sneak' is found in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'on' acts as a link.
Can you help me to learn more?
(Other definitions for sneaker that I've seen before include "Casual shoe" , "American trainer" , "Canvas shoe" , "Soft shoe" , "Trainer (shoe)" .)