Uproar engendered by American supporting scrum (6)
I believe the answer is:
ruckus
'uproar' is the definition.
(I've seen this before)
'american supporting scrum' is the wordplay.
'american' becomes 'US' (abbreviation for United States).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'scrum' becomes 'ruck' (I've seen this before).
'us' put after 'ruck' is 'RUCKUS'.
'engendered by' is the link.
(Other definitions for ruckus that I've seen before include "Rumpus. commotion" , "Row or commotion" , "Uproar - noisy disturbance" .)