Being forbidden from committing manslaughter or carrying the ball in a motorized vehicle would generally be considered obvious enough to be an unwritten rule in most sports.
But Shrovetide Football is not most sports, and its tiny rulebook, hilariously comprised of scarcely more than the broad regulations mentioned above, would alone be enough to qualify it as a contender for the title of craziest game in the world.
Yet that only tells part of the story of this extraordinary ancient competition from rural England, which claims to be the "mother" of all modern football codes such as soccer, football and rugby, and is finding a surprising new American following thanks to the release of a documentary film.
"Wild In The Streets" details the annual game between two halves of the town of Ashbourne, near the city of Derby in the English Midlands, which stretches over two days, beginning each Shrove Tuesday – or Mardi Gras in the United States.
"When we say the game is between two parts of the town, we are talking literally," local David Sullivan told Yahoo! Sports. "Pretty much anyone and everyone plays; there is no limit on numbers."
The object of the game is to move an oversize and ornately crafted leather ball toward the respective goals, a mere three miles apart. The competitors number in the thousands, so congestion makes moving the ball forward with any speed difficult.
A popular tactic is for groups of players to huddle together around the man with the ball and move forward en masse, creating a juggernaut of humanity seeking to trample through the other team's defenses.
The opposition will try its damnedest to hold firm, break up the movement and wrestle back control of the ball, and it is during these skirmishes that the most brutal action occurs, with eye gouging, punching and stomping all being known to occur.
Rumor has it that the violence has quelled a little in recent years, yet the locals still tell stories of broken ribs, blackened eyes, gouged and bloodied faces, and a wide assortment of other gruesome maladies as a result of participation.
Once a team reaches the opponent's "goal," the ball must be struck three times against its target, a millstone set into the River Henmore. Unsurprisingly given the length of the playing area, scoring is scarce.
The field does not have any of those annoying limitations like sidelines or end zones. It does, however, charmingly incorporate roads, traffic lights, brick walls and pavement, with even the trusty Henmore forming part of the fun.
The film, narrated by "Lord of the Rings" and "Game of Thrones" actor Sean Bean has opened to critical acclaim, and American thrill seekers and gap-year travelers are rapidly adding Shrovetide to their itineraries for European adventure.
"I actually heard about it first from a British exchange student," said Brody Smith, 20, of Long Beach, Calif. "He told me about how historically the games were full of fights and violence but that it has calmed down a bit.
"Either way, the movie was awesome, and I have added it to my bucket list. I don't know when I will go, but I will definitely do it one day."
Visitors from the States, or indeed anywhere else, are free to join whichever team they like but are restricted from scoring goals, which is reserved for those born within the confines of the town – with birth location in relation to the river determining team affiliation to either the Up'ards or Down'ards.
Those faint of heart should think about staying home though, according to director Peter Baxter, with even the origins of the game having a somewhat gruesome mythology.
"Some people believe the game began in pagan times [around 1,000 years ago] amongst farmers who chopped off a virgin's head," Baxter wrote in an email. "The farmer who stole the head back to his farm was assured of a good crop."
Fortunately, the head became a leather ball and evolved into the mass carnival that is seen today and is considered by locals and historians to be the mother to the lineage of all modern "football" games.
Shrovetide's popularity dwindled when various kings during the Middle Ages tried to stamp it out, believing it caused injury to archers and prevented them from concentrating on target practice. It was resurrected in the 19th century when, despite police resistance, the sheer weight of player numbers ensured a game took place.
"The police were powerless to stop the game, and it has survived in Ashbourne to this day," said Baxter, before cheerfully pointing out another of the game's quirks, the absence of any referee or umpire.
The Ashbourne locals are fervently passionate about their sport, and Baxter says that for many, it is more important than material possessions.
Successful players become local heroes in perpetuity and form part of the legend of a sport that in terms of tradition and longevity outstrips its more popular modern derivatives.
More popular content from Yahoo! Sports
• Robert Griffin III placing injury blame on Mike Shanahan?
• Hakeem Nicks' absence at Giants workout was not a protest
• Bears LB Brian Urlacher's retirement forced in part by blow to pride
• 49ers WR Michael Crabtree could miss 2013 season with torn Achilles