Patterns of Home Run Hitting in the Statcast Era
1 Intoduction
This paper provides a statistical look at the patterns of home run hitting during the history of Major League Baseball. Section 2 describes the general home run hitting patterns together with the famous hitters associated with the different peaks in home run hitting. Due to the recent surge in home runs, MLB appointed a committee to better understand the reasons behind this increase. Section 3 summarizes the conclusions from this committee.
Using the Statcast database, one has launch angle and exit velocity measurements for every batted ball hit between 2015 and 2022. Section 4 takes an exploratory view of these data. The focus is on the comparison of launch variable rates and home run rates across the Statcast era. Section 5 views these data from a modeling perspective. A generalized additive model is used to relate the home run outcome with the launch variables. One can learn about the properties of the manufactured ball for one season by this model fit, and use predictions from this model to explore changes in the baseball in future seasons. Figure 6 gives references to recent articles, blog posts, and Shiny apps on this particular view of home run hitting.
2 History of Home Run Hitting
2.1 Overview
There has been a steady increase in home run hitting during the history of Major League Baseball. The following figure displays the average number of home runs hit per team per game from 1871 through 2022.
Since the 1950 season, there have been three significant peaks in home run hitting, the first peak in the early 1960’s, the second about 2000, and the last peak in the recent seasons about 2019-2021.
The figure includes five vertical lines corresponding to the seasons of these particular noteworthy individual hitting accomplishments.
2.2 Statcast Era
We focus on the dramatic changes in home run hitting during the Statcast era from 2015 to 2022. The following table gives the home run totals for seven seasons excluding the shortened 2020 season.
| Season | HR Total |
|---|---|
| 2015 | 4909 |
| 2016 | 5610 |
| 2017 | 6105 |
| 2018 | 5585 |
| 2019 | 6776 |
| 2021 | 5944 |
| 2022 | 5215 |
Scanning the table, we see
- a steady increase in home run hitting from 2015 to 2017
- a sharp decrease in home runs in the 2018 season followed by a sharp increase in 2019
- significant drops in home run hitting during the 2021 and 2022 seasons
2.3 Historical Hitting Rates
To get a reasonable measure of home run performance, it is helpful to describe the primary outcomes of a plate appearance. When a batter comes to bat, there are three basic outcomes: a batter can strike out, he can walk, or he can put the ball in play.
The following figure shows how the the rates of the three basic outcomes have changed over the period from 1960 through 2022. A smoothing curve is drawn over each group of points to show the basic patterns.