I have always wondered why something like a molotov cocktail wasn't widely used in infantary combat, throwing a pot filled with a flammable liquid at a shield wall would most definitelly be enough to break formation.
Considering since ancient times there are accounts of ships using primitive flamethrowers to burn other ships, and even setting pigs on fire hoping they would run towards the opposing army to break formation, I assume people back then were fully aware of how fire could be used in combat and even had liquids that burned well enough to be used in this manner, so I wonder why something like this is never mentioned (as far as I know)
Non-naval, non-artillery incendiary weapons were used. Fire arrows, fire bombs (like Molotov cocktails), one-man flamethrowers.
However, the hand-thrown firebombs and one-man flamethrowers have a short range, and hand-thrown firebombs don't deliver much burning liquid. It's hard to carry many of them. So very unlikely to be a battle-winning weapon. Uncommon, not decisive, but not so novel as to encourage their description as a marvel, so little mention in contemporary accounts is to be expected.
For a later analogous case, consider the hand grenade. Grenades were used in 17th century battles, but you rarely see any mention of them in descriptions of battles.
However, there are some accounts describing the use of personal incendiary weapons. Jean de Joinville, The Life of St Louis has
Finally, they brought up a peasant, who threw Greek fire at them thrice. Once William of Boon caught the vessel of Greek fire on his buckler, for if it had set light to anything on him, he would have been burnt. We were all covered with the fire-darts that missed the serjeants.
There is a short world-wide summary of ancient and early Medieval incendiary weapons in the early part of Science and Civilisation in China, Vol. 5, Part 7 Military Technology: The Gunpowder Epic (about 30 pages).
throwing a pot filled with a flammable liquid at a shield wall would most definitelly be enough to break formation.
You can find modern video footage of rioters throwing Molotov cocktails at shield walls. Sometimes the formation breaks, sometimes the formation just moves 2 metres, and sometimes the formation is unaffected.