One of the things that was recognized at Towton and is discussed in Blood Red Roses is that foot soldiers in the field tended to work in groups and were very efficient killers. In some cases forward members of the group did little more than pull opponents into the group for those behind them to finish them off or cause an initial debilitating wound and allow rear ranks to deliver the kill. Since the forensic evidence is broken into three groups, premortem, paramortem and post mortem, archeologists were able to reconstruct the causes of death for the bodeis excavated. Interesting stuff and definately a well worth it read.
Tor, the picture of the SCA combatants look static because they are at lay-on and not yet engaged. Not a fair assesment of what is about to transpire. As the first blows are thrown it will quickly turn into the second picture. Though many SCA fights (tournaments and one on one pick-ups) tend to start off with alot of the weight on the rear foot (though the knight in red is standing forward and is bladed into the fight already at the lay on) with one opponent quickly taking the defensive and back stepping and the more aggresive pursuing. The poses then would tend to be a little more active. BUt I would argue that fighting using SCA swords is much different than what you would find with bladed weapons. Since the majority of the SCA kills are to the head and thus the defense will most likely be the shield and sword creeping higher and higher as opponents try to make that kill shot. I think some of the fighting you are now seeing within the "fechtbuch" community (i.e. Talhoffer, Fiore, Wallensteine, etc.) would more likely be that which you would find in a real medeival battlefield by professional soldiers. Since they can grapple and we in the SCA can't, it makes for a much different dynamic.
The combat seen during some of the melees like at Gulf Wars, Pennsic or Estrella has plenty of action in it and I've seen some pretty animated fights. There, because of sheer numbers and melee rules everything becomes a target from almost any angle. Again making for a much different dynamic in the fight in both offense and defense.
In reference to your original question, I'd pick up a copy of Drawing Comics the Marvel Way. There is a whole chapter there on the posing of characters and how action, force, etc can be illustrated in the pose. Sometimes what may seem like a heroic or exagerated pose is necessary because the end result (illustration, figure, statue) is a static thing, relying on the pose to convey the action of the moment.
Regards,
Mike