The game rules were clearly stacked in favor of the home team.

stacked 是动词 stack 的过去分词形式，stack 本意是"堆叠、堆放"。在比喻用法中，stacked against/for 表示"（规则、条件等）对某人/某方不利/有利"，这里指比赛规则被刻意设计得偏向主队。