Dating back to the mid-19th century, baseball has seen a long history of rule changes.
Odd conventions included games being played to 21 runs and batters choosing the height of pitches.
Even in the modern MLB, there are still weird rules on the books that will likely never be enforced.
Although "Three strikes, you're out!" is perhaps the most basic rule in baseball, the fundamentals of the great American pastime weren't always this clear-cut.
The sport likely derived from cricket and similar games played in England. Variations were brought over to the Thirteen Colonies, and by the early 19th century, baseball in the US was composed of a few regional styles with varying rules. The New York rules ultimately took precedence, codified in the "Knickerbocker rules" named after the Knickerbocker Base Ball Club.
This 1845 ruleset implemented many key standards that are still used today, such as the three-out inning, and later versions would come to serve as the basis for the National League and American League's rules.
The original Knickerbocker rules were full of vague guidelines, such as bases being "forty-two paces" apart and teams being permitted to choose players from the crowd if they didn't have enough members.
Needless to say, the sport would continue to evolve over the next 180 years into the multibillion-dollar industry we know today — the MLB reported $12.1 billion in revenue for the 2024 fiscal year, per Forbes. The New York Yankees alone are valued at $8.2 billion, leading Forbes to rank them the 10th most valuable sports franchise in the world in 2025.
Through two centuries of growth, the sport's rules have seen their share of oddities and flat-out strange conventions.
As the 2026 MLB regular season officially kicks off this week, we're looking back at 10 of the weirdest rules in baseball history, from 1840s regional rules to the current MLB rulebook.
Early on, fielders would throw the ball at baserunners for an out.
A lithograph of an 1860s baseball game between the Athletic Baseball Club of Philadelphia and the Brooklyn Atlantics.
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In pre-Knickerbocker-rules baseball, different regional styles would have fielders "soak" or "plug" the baserunner, which meant hitting them with the ball and resulting in an out. This was used in the New England regional variant known as the "Massachusetts Game" and others, per the Baseball Almanac.
Though this added an extra contact element to the game, the ball was lighter than it is today and featured a softer leather surface.
This practice was outlawed in the Knickerbocker rules, in which a fielder had to tag the runner for an out.
Pitchers were required to throw underhand.
A baseball player circa 1890 in Lake Chicago, Illinois.
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Pitchers originally had to throw underhand in the Knickerbocker rules, likely drawing inspiration from cricket players' "underarm bowling" techniques at the time. The Knickerbocker rules made a distinction between pitching and throwing, noting, "The ball must be pitched, not thrown, for the bat."
The rule stood in leagues for a few decades until changes allowed pitchers more freedom. According to the Baseball Almanac, the National League allowed pitchers to throw sidearm in 1882, and then with no limitations at all in 1884.
Games were played to 21 runs with no set number of innings.
A baseball game being played at a New England college campus, circa 1875.
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Per the original Knickerbocker rules, games were played until a team scored 21 runs, called "aces" at the time. This meant the length of games could vary substantially, and it was possible for a team to win with 21 runs without their opponents even getting to the plate.
Because of the rule, long games would sometimes end prematurely due to darkness, and it wouldn't be until 1935 that the first night game under electric lights would be played in the major leagues, according to the National Baseball Hall of Fame.
As a result, the 9-inning standard we know today was implemented into the Knickerbocker rules in 1857.
Fielders could catch a ball on the first bounce for an out.
An 1880s baseball card illustrating a fielder making a "good pick up."
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Contrary to the basic fundamentals of modern baseball, until 1864, the Knickerbocker rules allowed for fielders to catch the ball after one bounce or "bound" for an out.
In foul territory, the rule still stood until 1882, when it was changed to a regular fly-ball out by the National League.
Batters got to decide the height of a pitch.
Charlie Ferguson of the Philadelphia Quakers, 1885.
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While a batter getting to choose the type of pitch they want seems unheard of in today's game, it was once standard practice.
For roughly 20 years, the batter was required to request a "high," "low," or "fair" pitch upon coming up to bat. The pitcher would then have to throw accurately to this demand. The rule was disallowed in 1886.
It would take nine balls to walk a batter.
A wooden engraving shows a game between the Boston Beaneaters and the New York Giants in 1886.
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The history of balls and strikes wasn't always straightforward. Umpires would initially call "fair" and "unfair" pitches before strikes were introduced in 1858 and balls in 1863, per MLB.com. However, it took a whopping nine called balls before a batter would be sent to first base.
The number of called balls was gradually lowered in the National League until it became four in 1889, where it has stood ever since.
Flat bats were permitted for a period of time.
The New York Giants' Heinie Groh used a "bottle bat" in the 1920s, only a few decades after flat bats were banned.
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From 1885 to 1893, the National League allowed for the use of bats with a flat side. Players would mostly utilize the paddle-like bats for bunting, according to ESPN.
Though flat bats were eventually banned, baseball would see plenty of new, sometimes weird advancements in bat technology. Heinie Groh of the New York Giants hit with a "bottle bat," notable for its large barrel. And in 2025, the Yankees set a trend around the MLB with their "torpedo bats," which distribute the wood's weight in a favorable way for the hitter.
"Spitballs" were allowed until 1920.
Fans speculated that 1950s pitcher Lew Burdette of the Milwaukee Braves used a spitball decades after it was banned.
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A "spitball" is exactly as it sounds. Pitchers used to be allowed to lubricate the ball with saliva to get a better pitch.
While players did literally use their own spit, the term also applies to any foreign substance applied to the ball, such as mud or petroleum jelly. The pitch reached peak popularity in the early 20th century, and safety concerns led to its ban in 1920, per Twins Daily.
Oddly, the MLB still allowed 17 legacy "spitters" to continue to throw the pitch until their retirement. Pitcher Burleigh Grimes played in the major leagues until 1934, using the spitball until the day he retired.
In the current MLB rulebook, a provision notes, "No player shall intentionally discolor or damage the ball by rubbing it with soil, rosin, paraffin, licorice, sand-paper, emery-paper or other foreign substance."
Thanks to the legacy of the spitball, there's now an official rule against licorice in the MLB.
The umpire can declare the away team the winner if a fan lingers on the field for 15 minutes.
MLB umpire Jen Pawol.
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In the current MLB rulebook, a quirk exists under the "Security" section, which provides guidelines on stadium protection and the procedure for when a person or group enters the playing field during a game.
The penalty in the section reads, "If the field is not cleared in a reasonable length of time, which shall in no case be less than 15 minutes after the visiting team's refusal to play, the umpire-in-chief may forfeit the game to the visiting team."
Even if such a scenario were to occur, it would be more likely that the game would be suspended and completed at a later time, as is commonly the case with rain delays. Alternatively, games suspended after 5 innings can be deemed "official," with the current score standing as the final result.
Players on opposing teams can't talk to each other.
Mike Trout of the Los Angeles Angels talks with Los Angeles Dodgers shortstop Mookie Betts during Spring Training.
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Still on the books today, the MLB rule on "Fraternization" states, "Players of opposing teams shall not fraternize at any time while in uniform." Perhaps the most unenforced rule in the major leagues, it's broken on a nightly basis.
The rule also disallows players from interacting with spectators during or after a game. This means that anytime a first baseman tosses a foul ball to a wide-eyed kid in the stands, it's technically in violation of the MLB rulebook.