How do you get one going backwards at high speed?
Here's one recipe:
First get going at high speed at high altitude; 40,000 feet will do.
Then call "Turn in, Fight's on" and start a head on pass directly toward your adversary, usually one of your squadron mates. Pass as close to him as you dare and the instant you pass roll into a 60 degree (more or less) bank and pull back on the stick as hard as you dare to extract the maximum aerodynamic performance of your aircraft. The idea is to make as tight a turn as possible. If you do this while climbing your speed will decrease and allow a tighter turning radius.
At this moment you are right at the edge of the performance envelope which is a diagram with speed on the X axis and g on the Y axis. You airplane will be g limited by stall at lower speeds and structural limits at higher speeds and when you plot these limits the boundary looks like an envelope with the flap open. Hence the term "pushing the envelope" and all that.
Anyway, if you continue to pull back on the stick and go over that edge you will experience a "departure"; i.e. you will depart from controlled flight. It's hard to predict what might happen next but one option is that the airplane will "swap ends" and do a bit of backwards flying for a moment. Turbojets intensely dislike air being rammed up the tailpipe at high mach numbers and will frequently demonstrate that dislike by producing a compressor stall. This can be accompanied by loud and very scary noises, belching fire out the intake, and the poor pilot having another of those all too frequent chats with God.