First Blood

The Hero and the Villain face off in battle. They both pull their weapons and charge at each other. After the first blow we see a shot of the floor beneath one of the combatants. A stream of blood trickles down. This is a common way to show that the battle is serious and one of the characters is injured. Often the next shot will be of the injured party touching their wound and saying "I'm bleeding?" A common trope in any show that involves a lot of bleeding.

Got jack all to do with the first Rambo installment of the same name, or the sequel, First Blood Part II.

Live Action TV

 * In Firefly in the episode Out Of Gas it opens with a deserted ship and Mal staggering through the hold and falling to the ground. We only find out he's wounded when we see blood dripping through the deck underneath him.

Literature

 * In James Swallow's Warhammer 40000 Blood Angels novel Deus Sanguinius, it is a great shock to Arkio's forces when in his duel with Rafen, Rafen draws first blood. Especially to Sachiel, who realizes that the blood is tainted, and so Arkio must be.

Anime and Manga

 * This is common in Bleach, especially Ichigo's battles.
 * The final fight of the final episode of Cowboy Bebop had this for both combatants.
 * Saito vs. Shishio, Gatotsu Zero Style!
 * Elfen Lied at the beginning of the Lucy vs. Nana fight.

Comics

 * In an old issue of Spider Man, Peter slugs Venom in the face after being abandoned on a deserted island with his enemy. Venom actually bleeds and tells Spidey that he has "first blood".

Video Games

 * In the big knife fight of Resident Evil 4, Krauser's first blow gives Leon a shallow cut on his cheek, which stays for the rest of the game.
 * Emma inflicts this to

Film
"Don Diego: I needed that scratch to awaken me."
 * The Mark of Zorro:


 * Instead of finding horror in this, Bruce Lee gathers berserk strength by touching the wound licking his own blood off his fingers.
 * Played for laughs in Kung Pow: Enter The Fist. When The Chosen One and Wimp Lo's fight is stopped, Wimp Lo declares "he is bleeding, making him the victor."
 * Most Errol Flynn swashbucklers had moments like this.
 * In The Great Race, the great sword fight had a moment like this.

Professional Wrestling

 * This is the name of a gimmick match type in professional wrestling, in which the first person to bleed is declared the loser.

Real Life

 * In some fencing matches, the first person to draw blood is declared victor and the match ends.
 * The epee was created in response to laws that duels be to first blood instead of to the death, removing the sharp tip. Instead they had three prongs to gouge out a chunk of flesh. They did still want it to be obvious when someone was struck.
 * Other matches require that the blood be drawn from the torso to count as victory.

Tabletop Games

 * The card Sadistic Glee has a memorable line... "First blood isn't as important as last blood..."

Web Original

 * Noka is slashed by Abel of all people, and with a sharpened stick that was ripped from a bed frame.