Repercussions following US subject (9)
I believe the answer is:
aftermath
'repercussions' is the definition.
(I've seen this before)
'following us subject' is the wordplay.
'following' becomes 'after' (I've seen this before).
'us subject' becomes 'math' (mathematics).
'after'+'math'='AFTERMATH'
(Other definitions for aftermath that I've seen before include "Circumstances that follow as a result of something" , "What may be the later consequences" , "Wake" , "Frame that in following events" , "Repercussions" .)