To do so the wrong way will go against the grain (3,2)
I believe the answer is:
rub up
'grain' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rub up that I've seen before include "shine" , "Polish" .)