To be honest, nothing much can defeat a Swadian cavalry charge. They are fast, maneuverable, heavily armored, can generate enough force to push through at least a 3-thick heavy infantry wall, they have long weapons that can only be outreached by long spears, they can destroy both heavily and lightly armored troops, have large, strong shields that can withstand extreme force and can only really efficiently be broken by axes, lances or thousands of ranged weapons, they can devastate any troops on a hill not at least with a gradient of 1.5,1, they are extremely effective on foot or on horseback and they are almost invulnerable to anything but heavy blunt/chopping weapons. But they can be defeated. Now, what makes the Rhodok spear-wall so effective is their tight formation. Their heavy infantry remind me of the Romans, with their large shields and short swords. Also, their unique spear-shield combination in similar in design to that of the Spartans. They fight as one unit, and although they may not win a duel in a single combat with an expert warrior, there are few that can best a well-formed Rhodok shield wall. Now, back to the question in hand. A Swadian cavalry charge can decimate a Rhodok shield-wall. Generally. But I know a way. Have a few light cavalry units in your army, preferably low-tier Khergits and at least 5 horse archers. As I, and quite a few all-knight commanders have found while fighting the Khergit faction, it can be extremely annoying trying to fight horse-archers. They are faster than knights, more manoevrable and can ride away while they harry them with spears and arrows. They won't really be good for actually killing the knights, and they will eventually be killed if you don't withdraw them, but they will serve their purpose as distractions for the knights. This will give you more than ample time to find a good place to form a battle line. Once you have found a suitable place (preferably a steepish slope or the crest of a hill), arrange your spearmen in a 3 thick wall (don't worry, the slope will more than account for the horsemen's momentum), and tell them to use their weapons at will. When the knights do come at your troops, the slope will destroy their momentum, their most valuable weapon, and they will hit your wall doing 1 kill maximum (if they're lucky), and then once all their cavalry are stuck, tell your men to charge. The Swadians will generally attempt to retreat, do NOT let this happen. One or two spearmen will be more than enough to stop them from falling back (if they haven't gathered momentum yet). Your men will automatically surround them. The knights will possibly get a couple of kills, but as they have no (or very little) speed, they will not take too many of your numbers, also most of them use morning stars which are only effective with speed, and as such will not be as effective as they would be if they were at full speed on a flat or downward-sloped surface. But, your men will kill them quite soon as some of them (depending on your choice of troop) will probably have large double-handed blunt weapons. There you have it! One of the best anti-knight tactics you can find (I think). Of course, the whole process will be infinitely better if you have a couple of crossbowmen or longbowmen. Place them on a higher slope than your spearmen and just behind and watch the beautiful destruction!
Thanks for reading and good luck!
-Your friend and humble adviser, Ravenos