Please expand!
I assume you mean: "surely they all had lances if on horses, and had swords and axes if on foot, and just massacred each other..."
Yes, sure. I'm sure that's not inaccurate. Especially if they were rich knights, as is the romantic imagery.
However, consider the art of Street Fighting. And, of course, I don't mean "fighting in the street", nor anything to do with Street Fighter. Rather, the martial art of Street Fighting, which comprises a variety of different martial arts which are employed depending on distance to the opponent. For example, in the context of modern martial arts, in rough order of distance from the opponent, this may include fighting with sticks, knives, kick boxing, boxing, hand/arm blocks, grappling, wrestling/judo. And this may include other martial arts also, depending on preferences of the individual.
Perhaps the closest to this concept, in official capacity, is Jeet Kune Do.
In practice, the martial artist would learn all techniques, then decide which he/she is most naturally attune to. Then, they would focus on those particular techniques, and master them. In a practical fight, the martial artist would attempt to force the opponent into the correct fighting distance for the martial art(s) that they have mastered.
For instance, the art of Krav Maga, which Granville earlier mentioned, is a special case of this. However, in the case of Krav Maga, one person decided what was best for them, and then enforced all others to learn the martial arts in the same proportions suitable to him. This was not an unwise move, given that it was to be blanket-taught in a military capacity. However, for an individual case, it is a less-customised version of the general technique I describe above.
From my understanding and interpretation, I believe that this is indeed included in the principles of medieval warfare. Whilst we might associate medieval warfare with lances and swords, due to romantic notions of that time period, I believe that individuals that were less fortunate/armoured would have attempted to force the opponent into a position that would have left them weak to the aggressor's prime strategy. For example, what use is a knight with a sword in a wrestling match? Providing the aggressive wrestler can get past the knight's sword, into the wrestling distance! My interpretation is that such considerations are encompassed within the "Science of Defense" of the Middle Ages.