What would be the most efficient way to blunt a heavy cavalry charge? My characters are part of a larger unit wearing heavier armour and ready access to shield and polearms like spears, halberds, and the like. Would these tools assist in reducing the chance of being heavily disrupted?
The very short answer is: kill the horses. Heavy cavalry without horses are just heavy infantry. Still dangerous, still with a combat role, but nowhere near as threatening as they were on horseback.
This may sound callous, or even cruel, especially in a modern context, but it’s worth remembering that warhorses are equal parts weapon, and a member of the enemy forces. It is neither a pet, nor an innocent participant. It is actively trying to kill you.
Depending on the situation, the easiest way to deal with enemy cavalry may simply be entrenchment. Rows of sharp spikes mounted onto a log (called a Cheval de Frise) is one excellent way of making sure that enemy cavalry can’t simply charge into your forces. Improvised ones may be as simple as lashing crudely sharpened logs together.
In more offensive situations, making sure your front line, particularly along the flanks, includes squads equipped with polearms (usually spears or lances) can make the force far more resistant to incoming cavalry charges. If they deploy those weapons in a rough phalanx, the first line of any incoming horses will get skewered, and the ones that follow will have to navigate their own dead in addition to the battlefield. (Also worth noting that films have lied to you. Most horses, even war horses, will not willingly charge into readied spears, even if its rider orders it to.) These soldiers may be reinforced with heavy infantry, who can move in and replace them when the enemy infantry reaches the spear wall.
One primary value of cavalry is the ability to flank an enemy force. Somewhat obviously, the horse can move far faster on the battlefield, which more than makes up for the additional logistical concerns, and that, while traveling, heavy cavalry will actually slow the army’s movement overall. This means that effective use of the horse includes moving past the the enemy’s formation, and then strike from the rear, or sides of their forces. This can potentially result in a situation where both sides field flanking cavalry, who engage with one another out away from the main force.
Carefully deployed skirmishers can break up a cavalry charge before it gets started. Skirmishers are light units who may be deployed in advance of the main force, with the intention of disrupting and harassing enemy forces before combat begins. While it’s less of a sure thing, skirmishers armed with ranged weapons can begin softening up the incoming cavalry before the fight even gets started.
Mounted archers (and later mounted gunmen) were more of a specialized unit, so not every force fielded them, but they could be exceptionally useful in a skirmisher role, taking shots at enemy forces, while still maintaining their distance.
Terrain can also be an important factor to control enemy charges. Holding high ground, like a ridge, can make it much more difficult for cavalry to charge up to you. They’ll still be able to get there, but they’ll be far more exhausted by the time they reach you.
Dense forests can also be incredibly disruptive for horses, as it’s much harder to maintain formation when there’s a tree in your way. Combine that with uneven terrain, and it’s just a terrible place for mounted combatants.