Make no progress, in the main (5,5)
I believe the answer is:
tread water
'make no progress' is the definition.
(I've seen this in another clue)
'in the main' is the wordplay.
'in the' becomes 'tread' (I can't explain this - if you can you should give a lot more credence to this answer).
'main' becomes 'water main' (water main is a kind of main).
'tread'+'water'='TREAD WATER'
Can you help me to learn more?
(Other definitions for tread water that I've seen before include "Hold back from making progress" , "Make little or no progress" , "Stay afloat" , "unwilling to go with the flow?" , "Mainly make no progress" .)