How Effective were Spears Against Cavalry?

[Domen]

That a blunt instrument is effective against an armoured man seems not implausible

Crushing blunt weapons - the type of blunt weapons, designed to destroy enemy light and medium armor (chain mail, brigandine, karacen armour, laminar armour, etc.), without causing open wounds, but with a result of extensive internal injuries, which would effectively eliminate the enemy from combat. (...) Introduction of the rigid plate armour in the late Middle Ages reduced efficiency of existing crushing weapons. This in turn led to increased work on the development of crushing weapons.