Attackers taking out American cavalry? (6)
I believe the answer is:
riders
'cavalry?' is the definition.
'attackers taking out american' is the wordplay.
'attackers' becomes 'raiders'.
'taking out' is a deletion indicator.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'raiders' with 'a' taken away is 'RIDERS'.
(Other definitions for riders that I've seen before include "Jockeys" , "Travellers on bikes or horses" , "Clauses appended to legislative bills" , "Clauses appended to a legislative bill" , "qualifications" .)