The fans rallied together with shared feeling and cheered for the home team.
Tips
history
Fused from two classics: 《诗经·秦风·无衣》 "修我戈矛,与子同仇" (repair our spears, share this enemy with you) and 《左传·文公四年》 "诸侯敌王所忾" (the vassal lords share the king's indignation). 忾 (kài) here means righteous anger, not hatred in general.
mistakes
忾 is often misread as kǎi or qì. The correct reading here is kài (4th tone), a rare pronunciation preserved only in this chengyu.