Tuesday night MLB set a record strikeouts in a season, the seventh year in a row the majors set a new high. I thought this might be a good time to look at various hitting averages and how they changed over time to see why strikeouts might be increasing so much.

This spreadsheet covers the low mound era (or the division era) which started in 1969. The chart connected to the sheet shows the levels of K per PA, Batting Average (BA), Batting Average on Balls in Play (BABIP), and Slugging Percentage.

Strikeouts rise slowly over time during this era. They actually fall from a 0.152 K per PA in 1969 to a low of 0.125 K per PA which persisted from 1979 through 1981. Since then K per PA mostly rose, and by 2005 was up to 0.164 K per PA. From that time on, the slope increase greatly, bring us to the 2019 rate of 0.229 K per PA.

BABIP went through two stages. From 1969 through 1992, BABIP ran in the mid .280s. In 1993 BABIP jumped to .294 and since then trended in the high .290s.

Looking at the data, it strikes me that the sudden increase in BABIP was an adjustment to the increasing strikeout rate. Batting averages were depressed to around a league average of .256 from 1988 to 1992. As strikeouts rise, batting average will go down if BABIP and power remain constant. There are just fewer opportunities to get hits. At this time, the stigma of bulking up was disappearing, as players who built muscle hit just fine. Bulking up led to hitting the ball hard, which led to high BABIPs and higher slugging averages, and an explosion in offense. It’s astonishing how fast this transition occurred.

Likewise, the rapid rise in strikeouts from 2006 on was an adjustment to batters hitting the ball harder. It took batters a decade to figure out they hand to hit harder to make up for strikeouts, and then it took pitchers over a decade they needed to strike out many more batters to bring offense under control.

In the last few years both sides adjusted quickly. Pitchers keep upping their Ks rapidly, while batters adjusted this time by mashing balls out of the park. The gap between BABIP and BA keeps widening, but batters use power to make up the difference.

Note that when I use the term adjustments, I’m not talking just about the players. Front offices see what works, and will go adjust their rosters accordingly. Stronger batters worked in the early 1990s, so teams stocked up. Strikeout pitcher worked in the mid aughties, so teams stocked up on those types of pitchers. Now, launch angle and spin rate help determine who makes a roster. The league may adjust, too by changing balls or strike zone dimensions.

Pitchers get better and batters adjust. Batters get better and pitchers adjust. Usually it takes a lot of time, but it appears that as more data becomes available, the time to adjust has condensed.

Stay tuned, who know where the adjustments will lead next.