Fun With Hit Tracker: Home Runs Over Time
All home runs are not created equal. Over the course of a six-month season, things are bound to change. Players wear down or maybe some heat up. In the past, we've been able to find player trends by analyzing first-half and second-half splits or maybe even game logs. But now with new data sources, we can try to find out how or why players produce different outcomes over a season. Are they lucky? Do their skills improve? Do they fatigue?
Another great new data source that has not received the same attention as pitch f/x is Hit Tracker. Developed by Greg Rybarczyk, Hit Tracker tracks every physical aspect of the home run. So how did the distance of home runs vary over the course of the 2008 season?
The chart seems to show that home run distances trend upward until early August and then fall slightly. It also appears that we can say with confidence that over the course of a week, the mean home run distance will be right around 390-400 feet. The first data points on the chart are a bit whacky, since the March average was 399 feet per home run, but then the first three days of April averaged 390-foot homers per day. Hence, the five-day rolling average is somehow much lower than the same month's average. But the main observation is that from April until July, there is a rather distinct increase in home run distance—around five feet per dinger. So what causes the change? Perhaps players need some time to get into their groove, or perhaps the environment becomes progressively more conducive to home runs. But how do we measure that? Did I mention that Hit Tracker also records the two most important components a batter can control? It captures where and exactly how hard the ball is hit. With the upcoming advent of hit f/x, we might get this data for all types of batted balls. The launch angle is measured in horizontal and vertical degrees from the point of contact three feet above home plate, while the speed off bat is measured in miles per hour. I chose to use the speed off bat as a measure for the player’s skill over time. I believe that a hitter's objective when he is at bat is to hit the ball as hard as possible. Here are the results:
If it’s not the hitter who controls the change home runs, then it must be the hitter’s environment. Fortunately, Hit Tracker also records atmospheric effects such as temperature, wind, and altitude. Altitude should theoretically remain constant over time, as stadiums don't traditionally switch locations. But wind and temperature flow with the seasons. Since both factors can negatively impact the distance a ball travels, I plotted the absolute average impact as well as the actual average.
Putting it all together with the standard distance, which controls for atmospheric effects and simply measures how far the ball would have been hit in neutral conditions:
Looks pretty even throughout the season, with the exception that distance possibly curls up at the start and end points. This could all be contributed to small sample size, but the fact that better players make the playoffs may have something to do with it, but do better players also start out hot? I'll be sure to keep note of it over the next few weeks.
Here's a chart of the three year's worth of data. Out of about 15,400 homers, Hit Tracker was missing data on less than 300 of them. The table should be read as the mean of each category, followed by standard deviation in parentheses.
Month Amount True Distance Speed Off Bat Wind Effect Temp Effect Standard Distance March 26 399.8 (25.3) 105.6 (5.7) 5.4 (17.5) -4.0 (2.4) 396.7 (33.5) April 2214 395.6 (24.7) 106.1 (5.2) 1.7 (13.2) -2.5 (4.3) 393.8 (27.1) May 2522 396.0 (25.3) 105.6 (5.2) 1.8 (11.7) -0.2 (3.7) 392.1 (26.2) June 2545 396.6 (25.5) 105.1 (4.9) 2.0 (10.6) 2.0 (3.4) 390.0 (25.8) July 2446 397.9 (26.1) 105.3 (5.0) 2.3 (11.0) 3.3 (3.2) 390.4 (25.3) August 2641 397.0 (24.8) 105.9 (5.0) 1.4 (9.7) 2.7 (3.6) 392.7 (26.6) September 2508 398.0 (26.1) 105.9 (5.2) 1.5 (10.0) 0.9 (3.1) 392.7 (26.6) October 242 393.8 (24.8) 105.8 (5.1) 3.0 (10.6) -2.0 (3.4) 391.2 (26.7)
I wanted to do a mini-case study applying changes in home runs over time, and the clear choice for any such study is Ryan Howard. He gives us a nice sample to work with and such a large part of his value is built on home runs. He’s been on a clear decline since his age 26 season, so we can see whether there have been changes in his home runs year by year. Plus, if you look at his day-by-day graph on fangraphs, he’s been a rather remarkable second-half hitter.
Over his career, he's held a 168 point difference in OPS between the first and second halves of the season. I'm not predicting that he'll continue the trend this year—I'm just pointing out that the trend has existed.
Howard also intrigues me since I believe he might be the best opposite field power hitter of all-time. But that’s a subject I’ll tackle another time hopefully. Again I decided to forego the launch angles and stick to the effects of speed off bat, temperature, wind, and distance. Presented without much commentary:
Month Amount True Distance Speed Off Bat Wind Effect Temp Effect Standard Distance April 13 414.2 (27.3) 109.1 (5.1) 5.3 (12.5) -3.0 (4.3) 408.3 (28.9) May 29 394.9 (29.1) 105.7 (5.5) 3.4 (9.7) 0.5 (4.4) 390.1 (33.0) June 24 410.7 (32.9) 105.1 (5.2) 3.2 (11.4) 3.3 (2.8) 402.5 (30.9) July 28 398.1 (27.7) 107.7 (6.0) 2.8 (7.9) 3.0 (2.9) 391.2 (29.0) August 26 404.8 (30.8) 108.0 (6.9) -3.6 (13.2) 4.3 (3.0) 403.2 (35.0) September 30 400.2 (22.9) 106.4 (4.6) 1.0 (6.9) 2.1 (2.8) 396.8 (24.8) October 4 390.5 (25.0) 104.5 (6.5) 3.7 (4.5) -2.5 (6.3) 389.3 (32.2)
All data was obtained from Hittrackeronline.com. Interested parties may contact firstname.lastname@example.org