Does the velocity of the 4-seam pitch increase as the season progresses?

*This story was published on April 24th 2022 in Japanese.

Does the velocity of the 4-seam pitch increase as the season progresses?

The MLB season has been underway for almost three weeks now, and some players are doing well while others are not. Unfortunately, there are also players whose performance is not bad but whose future form is problematic. The best example of this would be pitchers whose velocity has dropped since last season.

Specifically, pitchers such as the Guardians starters (S. Beaver, C. Quantrill, and Z. Plesac) and Phillies’ Z. Wheeler, whom I posted about on Twitter last week, drops their average 4-seam velocity from the previous year.

Some people say even pitchers who do not have a high velocity in spring will rise the velo when the season progresses. So, for example, Robbie Ray, whose average velocity was 92 mph in the season opener, is up to 92.7 mph in his latest outing (still slower than last year).

In this article, I would like to test the hypothesis that “pitch speed will probably increase as the season progresses.

Before the verification, let me summarize the conditions for this verification.

The subjects of this study are 804 MLB players who threw at least one 4-seam pitch in 2021 (including fielders who pitched in the game).

What we can learn from the league average pitch speeds by month

In our initial examination, we look at the average 4-seam pitch velocity by month from April to September. First, we present the league’s monthly average pitch speeds.

The pitch velocity indeed increased as the season progressed from April to June after the start of the season. However, the increase is only in 0.1 mph increments, and the range of increase seems smaller than expected.

What can we learn from the average monthly pitch speeds of individual players

We have looked at the data for the league, but what is happening at the personal player level?

The graph above shows the percentage of pitchers whose pitch speed increased from month to month. Specifically, in April and May, there were 412 eligible pitchers (eligible pitchers were those who threw at least one 4-seam pitch in both months). Of those pitchers, 36 pitchers increased their pitch velocity by one mph or more, 8.74%.

From this graph, we can see that from April to May and from May to June, more than 65% of pitchers succeeded in increasing their pitch speed. On the other hand, from June to July and from July to August, less than half of the pitchers succeeded in increasing their velocity, indicating that more pitchers decreased their velocity.

What is even more interesting is that more than half (55.22%) of the pitchers increased their pitch speed again in August and September. This increase in pitch speed may be due to (1) a rebound from the drop in pitch speed during the summer and (2) pitchers gearing up for the final month of the season or with the playoffs approaching.

How long will the increase in pitch speed last?

I would also like to add how long the increase in pitch speed will continue.

The graph’s vertical axis above is the ratio of the number of pitchers whose pitch speed increased in May and June divided by the number of pitchers whose pitch speed increased in April and May (complicated, isn’t it?). Specifically, there were 269 pitchers whose pitch speed increased between April and May. Of those 269, 146 pitchers increased their velocity from May to June. Dividing this 146 by 269 yields a ratio of 54.2%.

This graph shows that more than half (54.28%) of the pitchers whose velocity increased in April and May also increased in May and June. Therefore, we can say that many pitchers continuously increase their pitch speed from April to June. However, many pitchers whose velocities increased in the previous month then decreased in the following month. Therefore, it is difficult for a pitcher to continue increasing his velocity for two months.

Comparison of Average Pitch Speeds in April and June

As we have seen, many pitchers increased their pitch speed from April to June. So let’s look at how much pitch speeds have risen during these two months.

The graph above shows the difference in pitch velocity distribution for the 377 pitchers who threw at least one 4-seam pitch in April and June, subtracting the pitch velocity in April from that in June. 92 pitchers on the 0.5 scale represent the number of pitchers whose pitch velocity increased by 0.5 mph or more but less than one mile.

As we have noted above, we can see again that there are many pitchers whose velocity increases from April to June. The most significant increase is on the 0.5 scale, followed by the 0 scales. Together, these two categories account for 176 pitchers, or a little less than half of the total.

Thus, from April to June, the average velocity of the 4-seam pitch increases for about 70% of pitchers, and the range of increase is often less than 1 mph, with an increase of 2 mph or more being extremely rare.