Something afoot for the coach
I believe the answer is:
'coach' is the definition.
(as in a sports coach)
'something afoot for the' is the wordplay.
I cannot really understand how this works, but
'something' could be 'er' (I've seen this in other clues) and 'er' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
The remaining letters 'rain' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for trainer that I've seen before include "Shoe; educator" , "Footwear singularly" , "Coach - one of a pair of shoes?" , "Person in charge of stable" , "Coach - item of footwear" .)