Crew crossing one watercourse displays standard (10)
I believe the answer is:
mainstream
'standard' is the definition.
(I know that standard can be written as mainstream)
'crew crossing one watercourse' is the wordplay.
'crew' becomes 'man' (both can mean to staff or operate something).
'crossing' indicates putting letters inside (to cross can mean to go over or around).
'one' becomes 'i' (Roman numeral).
'watercourse' becomes 'stream' (synonyms).
'man' going around 'i' is 'main'.
'main'+'stream'='MAINSTREAM'
'displays' acts as a link.
(Other definitions for mainstream that I've seen before include "Current" , "Relating to what is normal or standard" , "entirely conventional?" , "In accordance with what is normal or standard" , "According to Standard" .)