The call "Hats and Bats!" is one of the instructions used in the SCA for heavy fighters to Armour-Up, that is, to get your armour up to standards in preparation for battle at an SCA event.
When you hear "Hats and Bats!", quickly get your helmet on and your weapon in your hands, because the battle is about to start. No marshal likes to put two entire armies on hold to wait for laggards.