Darkhammer

The Ball and Chain knight is the Mini-Boss of the Snowpeak Ruins in Twilight Princess. when you defeat the creature it drops the Ball and Chain (not in a treasure chest) and you proceed to open the chest you  thought had the Big Key but really had Ordon Goat Cheese.

Perhaps this is in reference to A Link To The Past, in which Princess Zelda, imprisoned in a cell in the dungeon of Hyrule Castle, is guarded by a knight wielding a ball and chain. Upon defeating the knight, Link receives the Big Key.