One of the worst things a cavalry charge can encounter is a bulwark of troops in tight shield wall formation with spears leveled to impale anyone that gets close.

This exact maneuver is what the House Karstark Spearmen train relentlessly for, making them perfect for protecting flanks and rearguard of an army. The House Karstark Spearmen are a melee-centric, defensive unit. They are best suited to protecting flanks of an army, stopping enemy charges in their tracks as the unit braces for impact and pushes back any that would attack them.