The story
The noun is derived from brick + bat (“a bit, piece; specifically, part of a brick with one whole end”). The verb is derived from the noun.
Etymology from Wiktionary, CC BY-SA 4.0.
brickbat
brick·batToday it means: A piece of brick, rock, etc., especially when used as a weapon (for example, thrown or placed in a sock or other receptacle and used as a club). Full definition →