Esports / MOBA slang, calqued from English 'first blood' as popularized in DotA, League of Legends (英雄联盟), and 王者荣耀 (Honor of Kings). Heard in livestream commentary; rare in formal writing.
mistakes
Pronounced xuè in this gaming sense. Don't confuse with the colloquial reading yìxiě sometimes heard for 一血; gamer usage standardizes on xuè.