“The explosion knocked him out, but he was not seriously injured.”
When someone loses consciousness, usually due to being hit by something, such as a punch, we say they are “knocked out”. In an organized fight, such as a boxing match, it can be abbreviated to KO.
「爆発で気絶はしたが重傷ではなかった。」
人の拳など何かとぶつかって気を失う時は「knocked out」と言います。ボクシングなど正式な勝負ではKOに略すことがあります。