Demanding way in which rowing crew will replace American (7)
I believe the answer is:
weighty
'demanding way in which rowing crew will replace american' is the definition.
'weighty' can be an answer for 'demanding' (thesaurus). I'm unsure of the remainder of the definition.
'demanding way in which rowing crew' is the wordplay.
'demanding way' becomes 'wy' (I can't explain this - if you can you should give a lot more credence to this answer).
'in which' indicates putting letters inside.
'rowing crew' becomes 'eight' (crew of eight rowers).
'wy' placed around 'eight' is 'WEIGHTY'.
Can you help me to learn more?
(Other definitions for weighty that I've seen before include "Cumbersome" , "substantial" , "significant" , "Important" , "Heavy - very serious" .)