Many issues familiar to baseball fans came to light for more casual fans during this year’s playoffs, which provided some of the most entertaining games in the history of the sport. However, many of them might have been confused by the amount of bewildering terminology, and a strange tradition to throw home runs back that came to light during the playoffs and the World Series between the Los Angeles Dodgers and the Houston Astros.

From watching fans throw home runs back and slick balls, the playoffs this year drew great television audiences and provided fantastic games to watch, even for casual fans. For those who wondered what was meant by some of the issues, traditions and statistics, here’s a rundown of some of the most often-mentioned.

A good place to start is with a very unusual tradition.

Why Throw Home Runs Back?

This issue was all over the place after a Houston Astros fan threw a home run hit by the Dodger’s Yasiel Puig back onto the field at Minute Maid Park in Houston during Game 5 of the World Series.

The controversy came from the fact he snatched the ball away from another fan. Not cool. Although it turns out they were family.

But some might wonder – where did people start to throw home runs back? And why, when throwing the ball back on the field doesn’t do anything but cost the fan a souvenir?

It all started in Chicago, where a disgruntled bartender and Chicago Cubs fan threw back a home run ball hit by Hank Aaron in 1970 in Wrigley Field.

It turns out he had felt snubbed by Aaron the year before, when he caught another home run by the legendary hitter. When he tried to give Aaron the ball, Aaron walked away, apparently trying to get off the field quickly because Cubs fans had been throwing beer at him during the game.

From this unlikely beginning, the tradition continued. Cubs fans routinely throw home runs back that were hit by the other team, usually under pressure to do so by the crowd.

But even some Cubs fans think it’s, well, not a stellar tradition. “It’s stupid,” a Cubs fans told the New York Times in 2016. “Catching a home run is a once in a lifetime experience. Why should you throw it back just because it wasn’t someone on the Cubs who hit it?”

That could be a good point to consider for fans in both Chicago and Houston.

Slick balls

The issue of “slick balls” was mentioned in many media reports, often without explanation.

Some pitchers during the World Series complained that the balls were slicker than usual, leading to an inability to get the grip needed to throw an effective breaking ball (especially the sinker or slider).

Astros pitcher Justin Verlander and Dodgers pitcher Yu Darvish were among those who have mentioned the issue. Verlander said it was even hard to get the ink on some balls when trying to sign autographs.

Of course, that could explain the record number of home runs in the World Series.

However, physicist Alan Nathan with the University of Illinois said he doubts the slick ball theory. Nathan looked at the spin axis of thrown pitches in the series, particularly sliders, and compared them to the action of the ball from the season. He noticed no difference.

The balls also didn’t show any change in air drag, which is the force that slows a ball down as it moves through the air. He also noted what every baseball statistics fan already knew – the World Series is a small sample size for determining whether balls have been altered.

New Statistics

For people who tune in just to see baseball’s championship showcase, the number of statistics mentioned may have proved bewildering.

People such as this columnist complained about all the statistics that now surround the game. He especially pointed out wins above replacement and on base plus slugging percentage.

And that’s fine. Baseball is a game that can be appreciated on many different levels. If you just want to enjoy the drama, then by all means do so. The playoffs and World Series have provided plenty of that.

But, for those who want to know, here’s a brief rundown of four often-mentioned, kind of new statistics.

Wins above replacement

It’s simply a mathematical calculation for determining how valuable a player is over the average player at his position – in another, how many extra wins that guy gets you. The math behind it is complex, but you don’t have to know it to appreciate the final WAR number.

On Base Plus Slugging

On base percentage calculates how often a player get on base, by either hit or walk. Slugging calculates how many total bases a player reaches divided by at-bats. Combining the two gives you a great idea of how well a player gets on base, scores and hits extra base hits. A number above .900 is considered elite.

Exit velocity

The speed at which a home run ball leaves the stadium. The higher the velocity, the better the player is as a power hitter.

Launch angle

The angle at which the ball leaves the bat. Players today often try to launch balls higher because, statistically speaking, they have a better chance of getting a hit.

Those represent some of the most often mentioned baseball statistics and controversies mentioned this year. Keep this handy for next year. The way the past few seasons have gone, next year’s playoffs will only get better.