The fierce tribal loyalty among soccer supporters often leads to intense rivalry between fans.

tribal 是名词 tribe（部落）的形容词形式，后缀 -al 表示"与...相关的"。 tribal loyalty 字面意思是"部落式的忠诚"，这里比喻球迷对球队像部落成员对部落一样的强烈归属感和忠诚度。