what is meant by the idiom ( to drive first blood ) ?
I came across that expression in the movie Rambo and I want to know if that expression is a military expression in origin , and what is meant by it ??????????

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Hi 
I reckon this should be 'to draw first blood'.  In a fight, it is to inflict a wound on your opponent first, before they can wound you.

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Exactly what Neal said. Be the first to wound your opponent before they get you.

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Rambo uses this phrase to defend his actions to his colonel.  He is claiming self-defense, because the sheriff & deputies "drew first blood"---they started the battle by attacking Rambo first.

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Hi Nominee, Neal is correct.This idiom is thought to have come from the world of boxing. The expression is also used metaphorically to mean, "to score a victory over someone"
 eg In the debate, it was the visitors who drew first blood.
 We were hoping to draw first blood. Unfortunately, we didn't.
 "Draw blood" has a third  meaning as well. When you "draw blood" you succeed in hurting someone's feelings.eg The boy's scathing remarks clearly drew blood.
eg Sam's remarks were intended to draw blood.