Chainmail: the cover

The game's full title is Chainmail: Rules for Medieval Miniatures. That tells us exactly what the game is: a toolkit for simulating medieval warfare with miniatures on the tabletop.

The cover illustration shows a crusader knight (perhaps a member of a religious military order), clad in chainmail and helmet, striking with a sword from horseback. Opposing him are figures that appear to be Saracens, equipped with spears and shields.