Physics of Combat

"Why do we fuck the tree, ladies and gentlemen? We fuck the tree to get stronger, to get better, so that when your little arms get tired and noodly, you've tuckered out the enemy, too! So that when our champions go out to fight, when they do battle, they get a better chance to be the heroes you pathetic little wimps can only dream about being! And if you want to be one of those heroes? Well you're gonna have to light some candles, pay off a minstrel, put on your riding boots and fuck that tree like it paid your mother!"
~Ellayne Warbough, Sheriff of Alcedene
Scholars refer to the standard flow of a battle as the "physics of combat." Strategists and would-be generals study these and their various forms and nuances in depth to perfect their craft. In particular, clerics of Domielle are great repositories of information about this school of thought.
The basics of the physics of combat boil down to phases of a battle.
0. Officer's Mess. Before the battle actually begins, senior officers will gather to discuss reconnaissance, tactics, strategies, and maneuvers. Wise officers will set a rally point for the occasion of defeat, so the army can be rapidly reformed and either march home together or attack again.
1. Maneuver. In this phase, the combatants jockey for position, change formations several times, feel out enemy defenses, and try to collect whatever advantages that they can. During this time, light support and skirmishers will screen their armys' movements by spreading out in between the two forces. There they will fight the skirmishers of the enemy and seek to cause as much disruption as possible to the enemy. These skirmishers are essentially a distraction, and rarely a leader will expect them to do more than delay the enemy for a few precious minutes.
2. The Charge. This is one of two parts of the combat that everyone remembers at the alehouse when the war is over. This is when one or both sides have decided that their position is good enough and they charge the enemy lines. Disciplined troops do better on the charge, as undisciplined mobs have a tendency for their best athletes to run out front while the more average soldiers fall behind, leading to piecemeal butchery.
3. The Push. This is the part of the battle that the Ancient of War trains for. Shield to shield or pike to pike, the two sides will shove and push at each other while attempting to stab into the enemy. Despite the horrifying scrum, injuries are fairly light in this phase. Soldiers instinctively defend each other and aside from the occasional lucky shot, the angles and area is too tight for effective killing.
4. Valley of Shields. Eventually, shield or pike arms will tire. The natural instinct for a soldier at this point is to back up, and then the instinct spreads as the warriors on either side of them feel exposed and back up to maintain the line. A few parting swipes and tosses later, there is a no man's land roughly 40 to 60 feet wide between the two sides, far enough to avoid thrown weapons. Exceptional warriors will, having not been tired by the push, step out and challenge each other. They will fight in front of their armies while their comrades recover. Particularly successful champions will invigorate their men and restore their fighting spirit.
5. Repetition. The battle will likely repeat phases 3 and 4 several times.
6. The Retreat. Eventually, one side or the other will suffer a break in their will. A wise commander will withdraw in order when they sense that their men are flagging. A withdrawal in order is usually left alone, as attacking it is rarely worth the cost of a victory that is otherwise assured anyway. An unwise commander will attempt to force their men to press on regardless, and their break in will results in a retreat in disorder. A retreat in disorder, the lines break and panic spreads through the ranks. Particularly motivated or vicious enemies will then harry and attack the rear of the retreating force. This is where the majority of casualties will be inflicted if the victor's aim is slaughter. A particularly respected or charismatic commander may be able to snatch victory from the jaws of defeat by rallying their warriors now, reforming their lines and restoring enough resolve to continue the fight.
7. The Rally and the Rearguard. A force that rallies repeats steps 3 and 4 until one side breaks again. A force that is retreating will eventually leave a rearguard. Formed of the bravest and motivated to stop the slaughter, the rearguard will seek to buy the rest of the force time by making a stand. Traditionally, rearguards must be all volunteer.
8. The Aftermath. After one side owns the field, the other must return with at least one emissary under the flag of parley. They will ask permission to take their dead and negotiations may begin for ransom of captives, magic items, and specific valuables such as may have been captured such as battle banners, signet rings, lockets, or other such sentimental but low value items.