The Shape Of Baseball Is Changing In 2021

Image credit: Nick Madrigal (Bill Mitchell)

As the major league game undergoes drastic stylistic changes, the literal shape of the average major league regular is changing.

According to data shared by Baseball-Reference.com, the average height of regular position players in the major leagues, weighted by games started, peaked at 73 inches in 2016. It fell to 72.9 inches in 2019 and 2020.

The average weight of MLB regular position players, again weighted by games started, peaked at 211.4 pounds in 2015 but had fallen to 208.5 pounds in 2020. This could be reflective of a more youthful game, and younger players having lower listed weights earlier in their careers.

To that point, the average major league position player got a full year younger between 2010 and 2020, falling from 29.2 to 28.2 years old in that span. These numbers differ slightly from the public Baseball-Reference data because they are weighted by games started at the eight field positions, not including DH.

Baseball has not been consistently younger than it is today since the 1960s and ’70s, when multiple waves of expansion created opportunities for untested players. The average age of regulars in those decades got as low as 27.3 years old.

Presented below are takeaways from studying characteristics of major league regular players at various positions, weighted by games started and provided by Baseball-Reference.com. The 2019 season is used as a reference point because it was the last to feature 162 games under typical conditions.

 

Catchers

The probable advent of an automated strike zone in the major leagues will dramatically alter the shape of the catcher position. The ability to frame pitches as strikes will take a back seat to the more old-school catcher attributes of blocking, receiving and throwing. Teams may also begin to favor offensive production at catcher as they did in the 1990s and 2000s. 

Catchers in 2019 averaged 30.1 years old, which is on the extreme old side—86th percentile—for the position in baseball history. The average age of catchers has hovered between 29 and 30 since the mid 1980s, making it regularly the oldest position on the field.

First basemen

Given the high offensive production levels first basemen are expected to contribute, as well as the running and throwing limitations permitted, the position has skewed toward more experienced players in recent times.

The average age of regular first basemen was 29.8 in 2019, placing it in the 72nd percentile for oldest ever. First basemen haven’t been consistently young since the early 1990s.

Of greater note at first base is the diminishing requirement for height. A 6-foot player was once deemed too short to play first base, with exceptions made for the most prodigious sluggers, such as Prince Fielder. The reason for the height prerequisite was that taller players created larger targets and could stretch farther to receive throws.   

The tallest average height ever at first base was 74.8 inches in 2018. That figure dropped all the way to 74.2 in 2019, for the largest year-over-year decrease ever. Anecdotal evidence indicates that many non-sluggers under 6 feet tall, e.g. Michael Chavis, Jedd Gyorko and Tommy La Stella, have played the position with regularity in recent seasons. In another example, the Brewers shifted 6-foot Keston Hiura to first base.

Infielders

The average age of non-first base infielders was 27.6 years old in 2019. That ranks in the 20th percentile for youngest all time. The age of non-first base infielders fell dramatically in the 2010s as it declined from historically old levels in the late 2000s and early 2010s. At 29.4 years old, 2009 was the oldest average age non-first base infield regulars have ever been.

In particular, shortstop has been a young man’s position of late. The average age of regulars in 2018 and 2019 was 26.6, which is in the 6th percentile for youngest all time.

Second basemen are trending down from high average ages in the early 2010s. This is somewhat surprising in light of the slide rule at second base that disallows runners from sliding through the bag on double play pivots. The rule would seemingly allow older, less agile players to man second base.

Center Fielders

Based on the area center fielders must cover, the position has belonged to younger players throughout baseball history. Along with shortstops, regular center fielders are typically between 27 and 28 years old on average during most periods in history. This makes them the two youngest positions. 

Corner Outfielders

Corner outfielders are younger today than they have been throughout most of baseball history. The average age of left and right fielders in 2019 was 27.8 years old, which ranks in the 13th percentile all time in terms of youth. Corner outfield regulars had not been that young since 1977.

Not only are corner outfielders younger, but they are lighter than they have been since the late 2000s. This could be a distortion of the data based on younger players active today having lower listed weights early in their careers. Alternatively, it could indicate that youth and presumed speed are more prized on the outfield corners as more hard-hit fly balls are capable of doing more damage if not corralled.