Someone explain to me again what a "Castor Swing" is :S
Well, basically one of the mechanics of warband is that if two people are standing still, staring at each other, no one should be able to get off two swings in a row if they both have the best possible reaction time. So it's hit, block, hit, block, etc. When you throw footwork into the mix and turning into your swings, that's not really the case. What can happen is that when you go for your second swing if you turn into it, forcing the swing to connect early in the animation(Normally this would just glance, not even stunning your opponent), and they're also moving into the swing, you can get off two consecutive swings. Even if they blocked the first one, the second will still connect. There are counters to it, but the best thing to do is just to know when you need to block twice.
Anyway, there it is, the "Castor Swing". Stupid name, I think you can thank Allers for that, if not him then Cyranule.