I was wondering basically what the difference would be between individual melee combat styles and unit formation melee fighting styles in medieval and ancient times.
Was there any kind of technique in large scale melee combat like there was in individual combat or was it mostly just stabbing and slashing over your shield at opposing troops? Sorry if this is confusing I wasn't sure how to word it.
The most iconic formation before the Roman legion was the Greek Phalanx. There was no formal training for the Phalanx but every commander had to ensure his troops knew how to fight in this formation. For an example of single combat in this time we can turn to a Greek pottery, specifically the duel of Paris and Menelaus, which you can check out here Paris appears to be wielding a Javelin, while Menelaus appears to wield a Xiphos. The duel pretty much lacked "tactics" there were certain stances, but we only have treatises but there are only fighting treatises from the Middle Ages surviving to this day (that I am personally aware of at least.)
However after the Phalanx came the Roman legion, which allowed the romans to conquer all of their empire. One of the best things I've ever heard the Roman Legionary tactics being described to is a dance, however this comparison was when Caesar was fighting other legions, not when the Romans were say, conquering the Gauls. A majority of the tribes who the romans fought against didn't have any formal fighting styles, while the romans famously used the testudo and other formations. The typical Roman advance consisted of throwing javelins and then advancing before engaging in a melee with swords and shields. However duels say in the arena were different Gladiators were supposed to rival each other's strengths, for instance a strong gladiator would fight an agile one. Outside of the gladiatorial combat say between a Germanic tribesman and a Roman legionary who had for some reason decided to fight one-on-one with no legion behind them, the fight would just result in the victor being the better fighter.
The Middle Ages brought in a sorts of lack in tactical advance, the shield wall, Calvary charge, archer barrages and sieges, all pretty much remained the same. However duels changed a lot fighting treatises began to emerge and so more fighting "tactics" could be used. You can find full texts of a few fighting treatises here.
In conclusion while in a large pitched battle tactics can make or break battles, in a one-on-one duel personal ability as well as training can make all the difference.