I'll read between the lines of your post, and assume you mean "how do i shake someone from my six, who is roughly equal in speed with you and i don't have the room to reverse on him". I say this because anything other scenario is not nearly as dangerous. For example if someone's on your six but carrying 100MPH+ extra speed over you, then dislodging him is relatively easy and fairly safe (assuming you have speed to maneuver yourself). A simple break-turn, scissors, or a barrel roll defense works a treat and the latter two may even give you a counter opportunity. If they're on your six but significantly slower than you, then a spiral climb and/or rope type of maneuver could work well too. If you have enough room to reverse, you can often meet the bandit head-on and force a turning fight where you should be slower and will easily win angles on a bandit which is too fast if he tries to turn with you.
Ok, the real problem here is a bandit who is "saddled up". And the real answer is not to let them there in the first place. Seriously. Once they saddled up you will have limited chances for success. If they're a n00b, then you may stand a chance with some radical maneuvering, but if they have some AH experience, then more than likely your death warrant is already signed and delivered unless you can simply out-run them (aka run away). Improve your "SA" (situational awareness) and you will not have to worry about this situation so much.
So what maneuver could you try when someone is "saddled up" ? Well its not just a maneuver, its a whole strategy. Your aircraft model vs theirs is important here too, as is how much alt you have to play with, and what friendly support you may have around too.
The simplest case is you both have the same a/c or models which are very close in performance. The goal is to claw back some angles (eg force them off your 180 deg position) and hopefully while doing so create snapshot opportunities or force a complete overshoot. You can try a flat-scissors or a series of constantly changing plane barrel rolls. Remember to chop back the throttle as required and pop out flaps etc and skid with rudder to try create a speed differential which will progressively make it harder and harder for them to stay with you due to them getting out of phase with your turns etc. Look for a opportunities for snapshots and take em when you can. Any hits at this point can have important psychological impact on your opponent and/or may even damage or kill them. Eventually you become so out of phase that it will start to turn closer and closer into HO passes. At this point you have pretty much successfully taken back all your lost angles and are now on a more neutral footing and a more even fight can ensue. If you're in an F4-U then you can even drop the landing gear to help force an overshoot.
Other options are, if you're in a faster a/c, is to simply "tactically reposition" eg run away. You wont win any medals for bravery but you will have survived if nothing else. You can combine this with a reposition yourself closer to friendly aircraft who may well join in and save your bacon, or to some other form of support a carrier or feild ack (aka "ack hugging"). Now these aren't glamorous options and people may hassle ya on chnl 200 for ack running or simply running...
If you have some alt to play with there are a couple of other options. 1. the simple dive and zoom; 2. the spiral dive. If your opponent is in a slow a/c and your in a fast and heavier one. Then a simple dive to the deck can yeild good results against zekes, ki84s, N1k's 109s, and P38s. They cant dive very well, and if you time it right you can get them to commit to a dive they cant pull out off in time. Timing is everything. Or simply zoom up high, hammerhead over and pop em when their slower crate doesnt have the momentum to climb up to you. The 2nd option is a spiral dive. This is simply to enter a tight high-G spiral dive with throttle chopped 100% and flaps, gear, rudder skid, kitchen sink all out. If your opponent tries to follow and is less carefull in his speed control he will simply pop out in front of you as he wont be able to turn as tight as you let alone pull any lead to get a shot. You may even cause them to black out. The world is your oyster then.
Defensive moves from a saddled up position are at best desperate measures and you just hoping you can catch the other guy out, but you'd be suprise how often you actually can tho
Good luck.
