It’s finally Opening Day of the 2019 Major League Baseball season. Fans are already gearing up for six exciting months of their favorite sport, but opening day is also an opportunity for newbies to be introduced to the game by an already die-hard fan—or simply to discover why baseball is America’s favorite pastime.

The official rules of baseball can be surprisingly complex, and even the most committed fans can be baffled by an umpire’s call. This season, you can avoid the confusion and frustration that comes with not understanding a play with the Baseball Field Guide. This essential book, written by Dan Formosa and Paul Hamburger, is the go-to source for every rule in Major League Baseball—in plain English. It covers everything from the game’s basic rules to the most obscure ones, and the fascinating backstories that explain the rules you’ve taken at face-value.

Start this MLB season with the stories behind a few interesting rules you probably never knew:

Lena Blackburne Rubbing Mud

The rules require the umpire, on opening each sealed package containing a baseball, to inspect the baseball and to “remove its gloss.” This, by tradition, is accomplished by rubbing each ball with mud.

Since the 1930s, umpires have been using a very specific type of mud. In the 1910s and 1920s, Russell Aubrey “Lena” Blackburne played infield for the Chicago White Sox. He later was hired as the third base coach for the Philadelphia Athletics. In previous years umpires used a variety of substances to remove the shine from baseballs.

In 1938, Lena came across something that was perfect. Somewhere in New Jersey, at an undisclosed location along the Delaware River, he found a fine, chocolate pudding-like mud. The mud could be rubbed on a baseball, removing the gloss without discoloring it or otherwise affecting the ball. It worked perfectly. Within a few years every American League team was using it, and by the late 1950s, every team in the National League as well.

Lena Blackburne Rubbing Mud is still being collected from the banks of the Delaware River and is used by every Major League umpire today.

Note: While the rules call for the umpire to prepare the baseballs, today this task is typically carried out by the clubhouse attendant.

The Pat Venditte Rule
In 2008 Pat Venditte pitched an ambidextrous inning for the Staten Island Yankees in a Minor League game against the Brooklyn Cyclones. The last player he faced was Ralph Henriquez, a switch-hitter. Comedy and confusion ensued when every time Venditte switched pitching hands, Henriquez moved to the opposite side of the plate. It was a standoff until the umpires ruled that the batter must commit to one side of the plate before the pitcher was made to choose his pitching arm. A very angry Henriquez was subsequently struck out.

Weeks later, and because of the Venditte incident, the opposite ruling was adopted by Major League Baseball — the pitcher must commit first.

Righty or lefty… what’s the diff?
There are varying opinions about why same-handed pitches are harder to hit. Here are a few popular theories:
• Curveballs and sliders move away from a same-handed hitter, toward the outside of the plate. Most hitters have more success with pitches to the inside of the plate.
• Many batters say it is more difficult to track a ball moving away from them.
• Some batters claim it is more difficult to see the ball as it leaves the hand — especially when coming from a pitcher with a side-arm delivery.