Dueling Is Still Legal In These States
Walk five paces, turn around, take aim, and ... fire! If you hear the word "duel," this might be the first thing that comes to mind, a kind of Aaron Burr vs. Alexander Hamilton thing with those old-timey, single-shot pistols. Or, you might think of fencing-type duels, like the spectacularly accurate one-on-one fights in 1977's "The Duellists," Ridley Scott's feature-length debut film (available to give you an anxiety attack on YouTube).
Civilian death matches definitely seem like either Hollywood fiction or an artifact of a bygone era. The only legal, public fighting folks see nowadays is something like MMA, boxing, or maybe your kid's brown belt karate test. And make no mistake, dueling was completely legal across much of the world for hundreds of years. During the reign of King Henry IV (1589-1610) France alone saw around 10,000 duels featuring the famed, thin-bladed rapier for better stabbing (per National Geographic). Vikings were fond of duels to resolve disputes. Egil's Saga, a multigenerational Viking tale written down around 1230 CE (per the Literary Encyclopedia), features the main character Egil Skallagrímsson chucking his sword and shield down in frustration in the middle of a duel, lunging at his opponent, and literally ripping the dude's throat out with his teeth (excerpt on The Night Shift Guy). Suffice it to say, Egil won. Legally, too.
Dueling might not be as savage as this anymore, or employ rapiers. In two states in the U.S., though, it's still legal, provided specific conditions are met.
Calling it fair and square in Texas
First on the list is the U.S.' "go big or go home" capital: Texas. For a highly-romanticized state that — accurately or not — conjures visions of cowboys in spurs on horseback, Old West gunfights, and a defiant, authority-questioning attitude, it does make sense that Texas makes this very short list. But dueling in modern-day Texas isn't as simple as walking up to a guy, whacking him with your Stetson, and slinging your revolver out of your holster. It depends on a huge dose of very-Texan "you brought it on yourself, now deal with the consequences" common sense.
Taking a look at the Texas penal code, Title 5, Chapter 22. There's no explicit law stating that someone can challenge someone to a duel, and then follow rules x, y, z to see it to its conclusion. It's more that if you do get in a fight with someone, the whole kerfuffle can be called even (and non-prosecutable) if certain conditions are met, under Code 22.06, "Consent as Defense to Assaultive Conduct."
As Lawserver summarizes, the attacker had to have a "reasonable belief" that the victim consented to the whole thing. Also, the victim had to accept that the duel could threaten his or her livelihood, medical procedures, or "scientific experiment conducted by recognized methods." But, if the attacker inflicted "serious bodily injury," then the whole thing is off the table and we've got a crime, anyway. Cross gun duels off your list.
Dueling in the land of lattes and Microsoft
Ah, Washington. Gorgeous landscapes like Olympic National Park, endless Seattle coffee shops proudly sporting Nirvana posters, skyrocketing rents due to tech giants like Amazon and Microsoft, and of course, legal, knuckle-bleeding street brawls. While it might seem out of character for Washington to be the nation's preeminent duel-a-thon location, it makes our very short list for being even more duel-friendly than Texas.
The Washington State Legislature, Title 38, Chapter 38, Article 114, "Dueling," clearly states that anyone "who fights or promotes, or is concerned in or connives at fighting a duel" is prosecutable by law. So that's that, right? Not quite. It depends on whether or not a fight was planned, organized, or framed as a "duel," "Fight Club" style. This includes in public or in private. If this wasn't the case, we can look the Seattle government's penal code under Title 12A.06.025, "Fighting."
If two people fight in public and "create a substantial risk" to people or property not included in the fight, then it's illegal. Public places in this case include locations like "streets, sidewalks, bridges, alleys, plazas, parks, driveways, parking lots," and more. If no other people or property were hurt in these places, then the police have no reason to intervene because no laws were technically broken, as Breaking Grips further explains. This is partially how vigilante "superheroes" like Seattle's Phoenix Jones operated without prosecution. So if two folks agree to fight, between each other? Totally legal.