Batters had the right to request a low or high pitch from 1867 to 1887
Imagine Mike Trout walking up to the plate and telling David Price exactly where he wanted the ball. In the game's infancy, that was a reality: Prior to every at-bat, batters would request a high or low strike zone -- either from the knee to the belt or the belt to the shoulder -- and the pitcher had to put it there. Awfully demanding of you, late-19th-century batsmen.
One side of the bat was allowed to be flat from 1885 to 1893
Concerned about a lack of scoring in the National League (league-wide ERA: 2.37, so quit bragging, Kershaw), Cincinnati Red Stockings organizer Harry Wright proposed a rule change to help juice offense: Allow bats to have a flat face, much like cricket. After much hand-wringing, the NL adopted the policy in 1885, and, combined with changes to the pitching distance, runs began to increase -- until everyone soon realized that flat bats had a tendency to splinter, and the rule was rescinded in 1893.
Umpires in the 19th century had it made
The plight of the umpire is a difficult one: You try tracking a small white ball traveling at ridiculously high speeds, with a stadium full of people and the entire Internet ready to castigate you if you're wrong.
Being an umpire at the turn of the 20th century, though? That actually sounds pretty great: They were chosen from the crowd prior to first pitch -- they were often prominent members of the local community -- and rather than spend all that energy to squat behind the catcher, umpires were given easy chairs in the general vicinity of home plate. And that was just the beginning of the perks. From Ohio's Marion Star newspaper in 1916:
"The old time umpires were accorded the utmost courtesy by the players. They were given easy chairs, placed near the home plate, provided with fans on hot days and their absolute comfort was uppermost in the minds of the players. The umpire always received the choicest bits of food and the largest glass of beer."
Sign us up, please.
The spitball was outlawed in 1920 -- but pitchers who had been throwing it for years were grandfathered in
Pitchers doctoring baseballs was always an ethical gray area, but it was a fairly common practice in the early days, and spit wasn't nearly the worst of it: pitchers would use mud, grease, soap, anything they could think of to make the ball dance in unpredictable ways.
Wanting to bring more offense to the game, MLB responded in 1920, outlawing the practice for good. But several famous spitballers were in the middle of their careers, and so the league came up with a compromise: a grandfather clause, allowing those who had thrown it before the rule to continue to do so. Righty Burleigh Grimes carried the "last official spitballer" mantlefor 14 more years, grossing out all of his teammates until his retirement in 1934:
Ground rule doubles were actually home runs as recently as 1930
Yes, really: Any ball that bounced off the ground and over the fence was ruled a home run. Rumor has it that at least one of Lou Gehrig's home runs during his 1927 home run race with Babe Ruth was actually a ground rule double.
In fact, at one point the very concept of a home run was an alien one: According to Thorn, on May 21, 1880 -- a time when few parks had ground rules stipulating that a ball clearing the wall was a home run -- a player hit a ball over the fence and into a river, and the right fielder, confused as to what to do next, actually hopped into a boat to go retrieve the thing. (He eventually gave up, unsuccessful in his pursuit. Stay forever weird, baseball.)