Sabermetrics

The Evolution of Baseball

Baseball has undergone significant on-the-field changes over the past few years, due to the rise in the use of analytics by major league organizations for the purposes of player development, player evaluation, and on-field strategy. As summarized eloquently in an article by ESPN’s Buster Olney, starting pitchers are throwing fewer innings and being taken out of games earlier than ever before, pitchers in general are throwing harder than ever before, and hitters are taking more aggressive swings at higher launch angles in an effort to lift the ball in the face of defensive shifts and increased pitch velocity.

As a result, the game has changed in the following ways since 2002, as illustrated by five graphs:

  1. Three-True Outcomes, most notably strikeouts, have risen.Evolution of baseball analytics | True three outcomes
  1. Correspondingly, hitters have taken more of an “all-or-nothing” approach, as evidenced by the increase in hard-hit and soft-hit batted balls and the decrease in medium-hit batted balls.Evolution of baseball analytics | Batted-ball quality statistics
  2. Despite throwing harder than ever before, pitchers are throwing fewer fastballs and, as a result, fewer pitches in the strike-zone than ever before.Evolution of baseball analytics | Fastballs and fastball velocity
  3. Consequently, hitters are chasing out of the zone more often but swinging at pitches in the zone less often than ever before.Evolution of baseball analytics | Swinging out of the zone
  4. That being said, hitters have gotten better at hitting pitches out the zone, as evidenced by the increase in O-Contact, but overall contact rate has decreased because of the increased nastiness of pitchers’ stuff.

    Evolution of baseball analytics | O-Contact statistic

Given these on-the-field changes, I believe that the next natural evolution for hitters is the rise of the “selectively aggressive” approach at the plate.

In its purest form, the “selectively aggressive” approach would manifest itself in a hitter taking all balls but swinging at all strikes. Intuitively, this approach makes sense. After all, it is how every little-leaguer is taught to approach an at-bat: swing at strikes; don’t swing at balls. But it also makes sense in the context of today’s game. As an increasing number of pitches are located outside of the strike zone, it would behoove hitters to become more strike-zone conscious and decrease their chase rates. That being said, when pitchers do come into the strike zone, hitters need to be able to make pitchers pay.

As of May 10, there is a 0.19 correlation between the difference in a hitter’s Z-Swing and O-Swing% (“SA%”) and his wRC+, amongst qualified hitters. Here are the qualified hitters with the ten highest SA% so far in 2018, along with their corresponding O-Swing%, Z-Swing%, and wRC+:

Data from FanGraphs

The correlation between SA% and wRC+ is not perfect, but seven of the top ten qualified hitters in SA% have a wRC+ greater than 100, and two of those seven (Jed Lowrie and Leonys Martin) are not hitters that you would normally associate with having such high wRC+.

Evolution of baseball analytics | O-Swing% Z-Swing% SA% wRC+ statistics

Furthermore, amongst qualified hitters in both 2017 and 2018, there is a 0.14 correlation between the increase in a hitter’s SA% and the increase in his wRC+ from year to year. Here are the ten highest increases in SA% from 2017 to 2018 amongst 2017–18 qualified hitters:

Evolution 8

While Joey Votto is (in my humble opinion) the poster-boy for the selectively aggressive approach, Javier Baez and Nick Markakis, both of whom have had pieces written about them recently by FanGraphs’s Sheryl Ring, has perhaps gotten the most out of adopting the approach more often in 2018. Baez has increased his SA% by 10 points and his wRC+ by 55 points in 2018 (despite his BABIP decreasing by more than 50 points!), while Markakis has increased his SA% by 8 points and his wRC+ by 73 points.

On the surface, it seems as if Baez and Markakis could not be more different on the diamond (the former is an uber-athletic rising star, while the latter is a disciplined veteran). That being said, both Baez and Markakis are swinging at more pitches in the zone without chasing more pitches. It just so happens that Baez was already swinging at a lot of pitches in the strike zone in 2017 (73%) and is swinging at even more in 2018 (83%), while Markakis swung at a relatively few pitches in the strike zone in 2017 (59%) but has swung at more in 2018 (66%). For reference, the average Z-Swing% in both seasons amongst qualified hitters is 68%.

Consequently, both Baez and Markakis are having increased success in 2018 despite having chase rates at the opposite ends of the spectrum (Baez=46%, Markakis=24%, Average=29%). Thus, it is the selectively aggressive approach that links both hitters and is leading both hitters to more success. Specifically, Baez has decreased his strikeout rate by almost 9 points and increased his isolated power by almost 150 points, while Markakis has cut his strikeout rate by more than half, increased his walk rate by roughly 2.5 points, and increased his isolated power by more than 100 points.

Joey Votto of Cincinnati Reds
Joey Votto, the unofficial king of the selectively aggressive hitting approach (Paul Bereswell/Getty Images).

Nevertheless, even though Baez and Markakis have had more success in 2018 by swinging at more pitches in the strike zone, that is not all that is leading to success on a macro-level. As of May 10, there is only a .01 correlation between Z-Swing% and wRC+ in 2018. Rather, it is the selectively aggressive approach, that is, the combination of swinging at pitches in the zone and not chasing pitches, that is leading to more success. For instance, Andrelton Simmons has increased his wRC+ by 46 points and his SA% by 7 points in 2018, and he has decreased his chase rate and maintained his in-zone swing rate rather than increasing his in-zone swing rate and maintaining his chase rate, like Baez and Markakis.

It is yet to be seen if there are any diminishing returns to the selectively aggressive hitting approach. For example, would it be more beneficial (if beneficial at all) to swing at 100% of pitches in the strike zone and 0% of pitches out of the strike zone rather than 99% of pitches in the strike zone and 1% of pitches out of the strike zone? That being said, it seems as if that adopting the selectively aggressive hitting approach can reasonably lead to an increase in walk rate via swinging at fewer balls, a decrease in strikeout rate via swinging at more strikes and making more contact, and an increase in power via receiving and swinging at better pitches to hit.

Javier Baez Chicago Cubs swinging bat & Nick Markakis of Atlanta Braves running base paths
Javier Baez (left) and Nick Markakis (right), two early adopters of the selectively aggressive hitting approach? (Left: Jim Young/USA Today Sports; Right: Kevin C. Cox/Getty Images).

On the other hand, pitchers (and managers utilizing pitchers, pitching coaches coaching pitchers, etc.) are smarter than ever before. Fastballs get hit the most and the hardest, so fastball usage has decreased. Hitters have shown a willingness to chase out the strike zone, and pitchers are willing to oblige. Pitchers are using TrackMan data (i.e. spin rate, movement, tilt, etc.) to better sequence their pitches and/or tinker their pitch repertoires. Hitters have shown an advantage when facing a pitcher for the third time in a game, so managers are pulling pitchers before the third time through the order.

That being said, as pitchers have adjusted to hitters altering their batted-ball profiles in recent years, if/when hitters alter their hitting approaches to the selectively aggressive approach, the corresponding pitching evolution will be to make hitters miss in the strike zone rather than outside of it.

Obviously, that is easier said than done. But, hypothetically, the corresponding shift in value would be toward pitchers who throw strikes and get swings and misses in he strike zone. The following tables show the leaders in zone rate and miss rate in the strike zone so far in 2018, amongst qualified pitchers:

Evolution of baseball analytics | Pitchers in-zone percentage

Evolution of basebal analytics | Hitters miss rate percentage

Consequently, the value would be shifted away from pitchers who get hitters to chase and get swings and misses out of the strike zone. The following tables show the leaders in chase rate and miss rate out of the strike zone in 2018, amongst qualified pitchers:

Evolution of baseball analytics | Hitters chase percentage

Of course, I could be completely off-base, and baseball could evolve towards something completely different.

Gerrit Cole Houston Astros pitching
Gerrit Cole throws strikes and misses bats. Is he the future of pitching? (Mike Stone/Associated Press).

Thank you for reading. Please stay tuned for my next article, which will be about… a different topic.

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