16-4. 17-9. 12-8. 10-9. 19-2. 16-2. 19-4. These scores put together represent something closer to that of a football game than a Major League Baseball contest. All of these scores were recorded within the past week, dating back to the start of the second half of the 2019 season. Teams putting up double digit run totals for a single game is becoming a more common occurrence. Even by the 2019 offensive environment standards, things are continuing to even get more abnormal.
Back in April, I detailed the strong possibility of an even larger outburst of home runs coming in the near future (now), due to the combination of the juiced ball and the increased temperatures for games across the schedule in the months of July and August. Higher temperatures make it easier for the ball to fly, whether juiced or not.
Temperature increases across the country unsurprisingly correlate almost perfectly with the monthly league-wide rate of home runs.
League-wide HR/FB by month
My line of thinking was that the months of July and August would be a perfect storm for offensive production, reaching unprecedented levels, breaking records, and showcasing a brand of baseball that we’ve never seen. The main ingredients to this perfect storm mainly being the temperature and... the juiced ball.
Discussion about the state of the baseball was prominent during All-Star week. Justin Verlander made comments, Rob Manfred made a bad attempt at changing our minds, and so on. But with all this, the fact of the matter remains that there is something factually different with the baseball. Many people have referenced a research piece by Dr. Meredith Wills over at The Athletic and I will do so too.
While the 2017 home run surge seems related to thicker laces, that does not mean the 2019 ball has undergone the same changes, as there are a number of ways to improve aerodynamics. Three effects can cause a ball to travel farther: It displaces less air, it “wobbles” less, or it creates less turbulence. The first requires a smaller ball; the second relies on a more centered core; the third occurs with either a smoother surface or a more spherical ball.
The state of the ball for the 2019 season became apparent pretty quickly. Relative to historical standards for the month of April, records were made at the conclusion of the month. The league-wide HR/FB-rate was at 14.2 percent, crushing the previous record of April 2017 (another notorious year for home runs), which was 12.8 percent. Going into May, 2019 stood atop again, with the HR-FB rate standing at 15.1 percent, beating out May 2017 at 13.6 percent.
Fast-forwarding to July, we are now witnessing a ridiculous outlier. The HR/FB-rate for the month so far is 16.7 percent. The previous record for July was again, back in 2017, when it was at 13.6 percent. The new record currently stands at an astounding mark of 3.1 percentage points higher than the previous one. Making things more odd, the records of April and May beat out the previous record by only marks of 1.4 and 1.5 percent. In June, it took the top place by 0.7 percent. Throwing claims out is irresponsible, but the data would suggest that possibly an additional or further change has happened. A super-juiced ball, if you will.
To help visualize this, I separated league-wide HR/FB-rate numbers by month and year, only looking at the months of April, May, June, and July to give the 2019 season a fair comparison. Dating back to 2002, this put out a total of 72 months to look at. I then converted each monthly HR/FB-rate into a z-score to neutralize the impact of weather. To no surprise, the top month, by a considerable margin, was July of 2019 (the top four z-scores all came from the 2019 season also). July of 2019 was the only month to exceeded three standard deviations above the mean. The gap between the top z-score (7/19, 3.01) and the number two z-score (4/19, 2.68) was barely smaller than the gap between the number two and number four z-score (6/19, 2.32).
Top league-wide monthly HR/FB z-scores
So how has this abundance of home runs impacted scoring this month? How does it all set up historically? To start off, on a runs per batter basis, July 2019 beats out July 2016 far the biggest month for run scoring since 2002.
Top league-wide runs per batter by month
As for power in general, July 2019 sits at the top and no other month is close. It is probably safe to say this is the first month ever with a league-wide isolated-average over .190 too.
Top league-wide ISO by month
Now that we are more than halfway through July, what can we expect for August? Well... if historical trends remain the same, we can expect August to be an even bigger month for home runs and overall offense than this July, as shown in the first table above that HR/FB-rate peaks in August.
The best/worst is yet to come.
Patrick Brennan loves to research pitchers and minor leaguers with data. You can find additional work of his at Royals Review and Royals Farm Report. You can also find him on Twitter @paintingcorner.