Home Run Hitting

Jim Albert

Introduction

Historical View of Home Runs

  • Baseball Reference provides the average number of Home Runs, Hits, Runs for each team each game during all seasons of Major League Baseball (1871 through 2023)

  • Home Run hitting has gone through many changes in MLB History

Avg HR Hit Per Team Per Game

Seasons of Famous HR Hitters

Some Famous HR Seasons

  • Frank (Home Run) Baker (1914)
  • Babe Ruth (1927)
  • Roger Maris (1961)
  • Mark McGwire (1998)
  • Barry Bonds (2001)

Home Run Baker

  • Played during Deadball Era
  • Was home run leader in 1914 with 9 HR
  • Home runs were not a big part of the game

Babe Ruth

  • With Babe, home runs became a big part of baseball
  • Was home run leader in 1927 with 60 HR
  • Maybe the greatest player of all time

Roger Maris

  • Broke Ruth’s record with 61 HR in 1961
  • Played with Mickey Mantle
  • Some controversy with record (famous asterisk)

Mark McGwire

  • Played during “Steroids Era”
  • Competed with Sammy Sosa in 1998 for the HR crown
  • Hit 70 to break the record

Barry Bonds

  • Played during “Steroids Era”
  • Broke the HR record with 73 in 2001
  • Career HR leader with 762

HR Totals in the Statcast Era

Season Home Runs
2015 4909
2016 5610
2017 6105
2018 5585
2019 6776
2021 5944
2022 5215
2023 5868

A Plate Appearance

Three Basic Outcomes:

  • Strikeout
  • Walk
  • Ball put into play

How have the rates of these three outcomes changed over the last 50 years of baseball?

History of In-Play, SO and BB Rates

History of Rates

  • SO Rates have been steadily increasing

  • In-Play Rates have been decreasing

  • Pattern of Walk Rates are less clear, show up and down movement

In-Play Rates

  • Define the home run rate as the fraction of \(HR\) among all batted balls (\(AB - SO\))\[ HR \, Rate = \frac{HR}{AB - SO} \]

  • Look at history of \(HR\) rates

History of HR Rates

What is Causing the Increase in Home Rate Rates?

MLB Committee

  • Fall of 2017 a committee was charged by Major League Baseball to identify the potential causes of the increase in the rate at which home runs were hit in 2015, 2016, and 2017.

  • Report was released in May 2018.

Possible Reasons for Increase in HRs

The batters?

  • Changes in characteristics of batted balls
  • Launch angle, exit velocity, and spray angle

The pitchers?

  • Changes in types of pitches
  • Pitch location

Possible Reasons for Increase in HRs

The ball?

  • Changes in how the ball is made?
  • Seam height, core?
  • Drag coefficient?

Possible Reasons for Increase in HRs

Game conditions?

  • Ballpark effect
  • Weather
  • Cold vs. hot temperatures

Process of Hitting a Ball

  • IN-PLAY: Have to put the ball in play

  • HIT IT RIGHT: The batted ball needs to have the “right” launch angle and exit velocity

  • REACH THE SEATS: Given the exit velocity and launch angle, needs to have sufficient distance and height to clear the fence (the carry of ball)

Committe’s Findings (2015-2017 Data)

  • Found modest changes in launch angle and exit velocity among batters
  • Focused on RED zone – launch angle in (15, 40) degrees, launch speed between 90 and 115 mpg
  • The RED zone balls are showing more carry – they travel further

Committee’s Findings

  • Increase in home runs is due to better carry (less drag) for given launch conditions
  • Likely due to the aerodynamic properties of the baseball
  • Didn’t appear to be a property of the manufactured baseballs
  • Recommend that MLB monitor the climate environment of the baseballs

Recent Exploration of Home Run Rates

End of 2023 Season

  • Nine seasons of Statcast data (2015 - 2023) are available
  • Have launch speed and launch angle measurements for all seasons
  • Take a broader perspective on home run hitting

Empirical Approach

  • Look at region of launch angle and exit velocity where most of home runs are hit
  • Look at rate of batted balls in this region – how does it vary by season?
  • Look at rate of home runs for balls hit in this region – how does it vary season?

Launch Vars Where Most HR are Hit (RED Zone)

Balls in Play Rate

  • Interested in rate of “home run likely” (RED Zone) batted balls \[ BIP \, Rate = \frac{HR \, Likely}{BIP} \]
  • Are batters changing their approach?
  • Players getting stronger?

Rate of Balls Hit in RED Zone

Rate of Balls Hit in RED Zone

  • See a general increase in “home run likely” rates over Statcast period
  • Players appear to be changing their hitting approach or they are getting stronger

Home Run Rate in RED Zone

  • What is the chance of a home run given good values of launch angle and exit velocity? \[ HR \, Rate = \frac{HR} {HR \,Likely} \]
  • Characteristic of the baseball
  • Changes in drag coefficient over seasons?

Home Run Rate in RED Zone

Home Run Rate in RED Zone

  • General increase from 2015 to 2017
  • Big dip in 2018, followed by big increase in 2019
  • General decrease from 2019 to 2023
  • Interpretation

Focus on Two Seasons: 2021 and 2023

Season Home Runs HR Per Game Per Team
2021 5944 1.22
2023 5868 1.21
  • On the surface, the two seasons were similar with respect to home run hitting.

A Closer Look

  • Divide region of launch angle and exit velocity into subregions
  • Focus on 2021 and 2023 seasons
  • Look at changes in batted ball rate and home run rate in each region
  • Use logit scale

A Logit

  • If \(P\) is a rate, then the logit of \(P\) is \[ logit \, P = \log\left(\frac{P}{1-P}\right) \]

  • When comparing two rates, say \(P_1\) and \(P_2\), better to compare on logit scale:\[ \log\left(\frac{P_2}{1-P_2}\right) - \log\left(\frac{P_1}{1-P_1}\right) \]

Why Logit?

  • Proportions have a variation issue – proportions near 0 and 1 have smaller variability than proportions close to 0.5.

  • Logits tend to fix this variability issue.

  • Logits have similar variability across all proportion values.

Logits Stretch the Scale for Proportions Close to 0 and 1

Interpreting Difference in Logits

  • Suppose we compare two seasons \[ \log\left(\frac{P_{season \, 2}}{1-P_{season \, 2}}\right) - \log\left(\frac{P_{season \, 1}}{1-P_{season \, 1}}\right) \]

  • If the difference is positive, rate is higher in Season 2

  • If the difference is negative, rate is lower in Season 2

Example - Comparing 2021 and 2023 Rates

  • Divide launch angles from 20 to 40 degrees into 4 bins

  • Divide exit velocities from 95 to 110 mph into 3 bins

  • So there are 4 x 3 = 12 subregions

  • Compare 2021 and 2023 Batted Ball Rates in each region

  • Compare 2021 and 2023 Home Run Rates in each region

Comparing Batted Ball Rates

Comparing Batted Ball Rates

  • Some increase in batted ball rates in 2023 (compared with 2021) for high exit velocities and launch angles smaller than 30 degrees.

  • Harder to compare batted ball rates in two seasons for launch angles larger than 30 degrees.

Comparing Home Run Rates

Comparing Home Run Rates

  • For most of the bins for 105 mph or smaller, there was a smaller home run rate in 2023 compared to 2021.

  • This is especially apparent for exit velocities between 100 and 105 mph.

  • A dead ball was used in 2023 (relative to 2021).

Comparing 2021 and 2023

  • On the surface, home run rates were similar in two seasons.

  • But we see an 2023 increase in rate of “home run friendly” batted balls.

  • This increase is offset by use of a slightly deader ball in 2023.

Concluding Comments

  • Many factors influence home run hitting.

  • Two important factors are the hitters (values of launch variables) and the ball (carry or drag coefficient).

  • It is helpful to monitor the Balls-in-Play and Home Run rates to see the effects due to the hitters and the ball.

Concluding Comments (Continued)

  • Batters are stronger and changing their hitting approach, leading to higher rates of “HR friendly” balls in play.

  • The composition of the ball has gone through dramatic changes during the Statcast era.

  • Currently the ball is relatively dead compared to previous seasons.