This post might need graphics, I may add them later.
Overruns are a pretty rare thing in Belegarth. Most attempts end up meeting a line that is too well prepared, or the charge is too disorganized to have much effect. Armageddon gave me a few opportunities to witness and participate in a number of full on charges. Since it isn't common, now seemed like a good time to jot down some thoughts.
The most common charge, beyond a single person rushing, is a section trying to overrun the enemy. Big shields, lots of armor, and a bit of coordination can make it fairly effective. Even if they only reach a stalemate, there is good potential to get a few people through the line towards those pesky archers. I've seen it work here and there, but the risk is pretty high. If the sectional charge fails and suffers high casualties, their line ends up having too few numbers to hold back the remaining enemies. It can also cause a staggered gap next to the rushers, allowing someone to get behind your line.
The truly rare sight is the entire line/unit/realm charging head first into the enemy. Groups with less armor and experience tend to get cut down before doing too much damage. Even when they have much greater numbers, a more experienced group will do a decent job of countering them through maneuvers and good fighting.
So how is this ever going to be a successful strategy? Well, it seems to me that coordination is the main factor. Few groups have the cohesion to rally behind orders quickly enough to avoid being strung out here. Section charges are often intended to be more of a wedge, but your whole line can't do that without essentially allowing the enemy to form a kill pocket around your charge. As long as everyone pushes together and keeps a strait line, you'll see much more success.
Timing, as it so often is in this sport, is essential. Starting the charge too early in the maneuver phase of the battle gives the enemy time to change position and react to the charge. Too late and the lines have already reached the stalemate phase and your charge has less momentum. There isn't really an exact moment that is best, other than perhaps just before they raise their guards,just before reaching the stalemate phase.
If everything goes to plan, and the line reaches the front at the same time, it is up to each individual to try to push through and kill what they can. Part of the trick is making sure you are guarding your side with your shield, at least once you are inside the tip of their spears. Focus on quick kills and weapon arms. The more damage you cause, the less risk to you and the rest of your line.
Defending against this type of charge is a pretty broad topic. Plenty of options. You could always just charge them and have mass chaos in the middle. But really what beats a charge is maneuvering. Shifting the whole line to one side or backing away can cause the enemy to stagger and lose their punch. Thinning the middle while they fight defensively and pressing the flanks will likely get the enemy stuck in a kill pocket or even fully enveloped.
I've also seen a few sacrifice themselves to stifle the charge. By a handful of people charging in, the enemy has to slow down and deal with them, allowing the friendly line to step up and line fight, rather than suffer the full charge. With any luck, those that pushed in will stay alive long enough for their team to come to the rescue.
Moral of the story, trying to overrun the enemy is fun, but has a good deal of risk. Sometimes it is necessary, like when trying to avoid fighting two groups by pushing through one of them. Also, makes for great video.