It's a classic reversal move, done by forcing and capitalizing on an overshoot. It hinges on managing the closure rate between you and the enemy, and having excellent timing. I learned it by studying Drex's old films on BK's site.
(You really learn to appreciate it when you watch Drex use it to toast 5 guys in an A20).
It goes like Urchin said. You let your higher-E opponent approach from your six.
At about D2.0 or 2.5, you begin a gentle bank to one side, so that the enemy is flying directly at your lift vector (perpendicular to the top surface of your wings). At about 1000 yards, level out, and when the enemy gets within firing range (usually at about 600 yards), you pull up into a tight yo-yo, coming down on his six as he passes under you. You then have a limited window to take your shot. The better your timing is, the longer an opportunity you have.
A lot depends on initial closure rates. If the enemy is approaching too fast, go into a shallow dive as you bank to gain some speed. If he is approaching too slow, chop your throttle during the bank. Ideally (if you have some alt), again go into a shallow dive, but throttle down to maintain speed while your enemy accelerates by diving at you.
This move works best if the enemy pulls into a zoom climb after passing you as he'll slow down and give you a better firing opportunity.
There are two ways to counter this. If you notice too late that your enemy is reversing you, (ie, you went for the shot on the initial pass), the key is to immediately extend in a shallow dive rather than go into a gentle zoom or yo-yo. This takes advantage of your speed to put you out of easy guns range. The problem with this is that the enemy has plenty of time to set up another reversal when you come around again, and if the pilot is good, he will continue doing it pass after pass until you've bled away your energy, or until you get frustrated and make a mistake.
The second way is to predict the move when you see the gentle bank and prepare for it - be very aggressive. Instead of taking the snapshot, pull hard into a high-G yo-yo and try to saddle up rather than overshooting. Chop throttle if neccessary. Don't give your enemy time to prepare a reversal, manage your E and pull for a deflection shot, dictate control the engagement, don't give the other guy time to plan his next move. Lengthy BnZ passes will only benefit the pilot who knows how to use the reversal. The key is staying on top of him when he expects you to extend, you'll have a better chance of catching him in a low-E state where he can't maneuver very well.
