A rotor chopper assembly including a chopper rotor having a mounting lug. A knife blade includes a body having an opening arrangement configured to receive a retention device securing the body to a member that is rotatably connected to the mounting lug of the chopper rotor. During unobstructed operation of the rotor chopper assembly, the body is centrifugally urged radially outward from the mounting lug. In response to the body striking an obstruction during operation of the rotor chopper assembly, the body is urged into rotational movement until the retention device abuts a stop formed in the mounting lug. An angle subtended between axes defining unobstructed operation and stop abutment is different for at least two openings of the arrangement of openings formed in the body.