Ready for a fight (6)
(Other definitions for shadow that I've seen before include "Darker part" , "Secretly tail someone" , "Dark area from which light is blocked" , "Trail" , "Trace - dog" .)
(Other definitions for arm that I've seen before include "One fired" , "Limb; weapon" , "Test of strength with elbows on the table" , "Prime" , "Shoulder to fingertip" .)