How Have Pitchers Changed Over Time?

Just like how offensive profiles for each position have changed over time, so have pitcher's profiles for both Starters and Relievers. The offensive changes are due to both era and philosophy changes meanwhile the pitching changes are mainly due to philosophy changes. These philosophy changes are due to analytics showing teams and pitchers how to optimize their performance. Using Baseball Reference and Fangraphs data let's see how pitchers have changed and then what philosophy changes caused the optimization of players.

This graph shows the innings relationship between starting pitchers and relief pitchers over time. Since there is a somewhat limited number of innings each year one should assume that as one increases the other decreases. Rather, relief pitchers' innings have increased since 1920 while starting pitchers' innings have had major fluctuations. These fluctuations in starting pitchers' innings are due to the fluctuations in the number of games played each year. The relief pitchers' innings increasing despite these fluctuations displays the increased reliance on relief pitchers. After 2000 the fluctuations stop so we start to see a consistent relationship between relief pitchers and starting pitchers. With this consistency we can also the starting pitchers' importance has decreased while relief pitchers have increased. Though just looking at the inning on the whole doesn't tell the full story.

The top graph illustrates starting pitchers' average innings per start since 1980. As the years progress in this graph the average innings per start decreases. Now the drop from 1980 to 2023 may only be a little more than one inning but that still is pretty significant. That one inning less means that the bullpens now cover 11% more of the game. This puts significantly more strain on the bullpen day in and day out. This fact is illustrated by the bottom graph which shows the average number of pitchers used per game. From 1980 to 2023 the pitchers per game increased by about 2.5 pitchers. When you only have 8 pitchers in your bullpen teams are now using an additional 31% percent of your bullpen which is simply not sustainable. This issue is only further exacerbated as managers pull out all the stops to win the game. On the whole these two graphs further explain the impact of innings drop in starting pitchers as a result of the philosophy change but aren't the only result,

This graph displays the change in K per 9 over time for both starting and relief pitchers. K per 9 is the number of strikeouts (known as K's) a pitcher gets on average for every 9 innings they throw. Both starters and relief pitchers have seen an increase in their K per 9 since 1920. Though now relief pitchers have a higher K per 9 than starters. These increases are occurring due to analytics teaching teams how to make the best pitches and then teams show and implore pitchers how to throw those nasty pitches. This nasty stuff enables pitchers to keep hitters more off balance leading and pitching for strikeouts. While this is a result of analytics this is also one of the major catalysts for all the other effects.

The other main catalyst is pitch counts which this graph displays by showing the number of times pitchers have thrown in the 100-119 and greater than 120 ranges over the years. Now the 100-119 pitch range increased from 1980 to 2010 though at the same time, the number of innings starting pitchers threw on average decreased. This is where strikeouts factor as the number of strikeouts increases the number of pitches mostly likely also increase. And during this starting pitcher strikeouts increase one could surmise that it was talking pitchers more pitches to get through fewer innings. Now after 2010 we start seeing a decrease in 100-119 and both ranges combined. This is because teams became afraid of the injury risks of throwing too many pitches and with the more strikeout you to those danger pitch counts more quickly. Additionally, from analytics teams were able to see how dangerous facing a starting pitcher three times is so they figure it's better to throw a new pitcher. These two facts have directly increased pitchers per game and decreased innings per start. Now why teams choose 100 pitches as the danger number and not anything remains unclear. For all we know they could have picked it because it's a round number.

Through these graphs, we can see the philosophy changes have stemmed from the evolution of analytics. From analytics, pitchers have become optimized through becoming more strikeout-reliant teams and less likely to get beat due to seeing a pitcher a third time through (bc they don’t). Teams also have become more and more afraid of injuries. This has led to fewer innings for starters and per start while more pitchers per game and innings for relief pitchers. Now whether these changes are good for the game remains to be seen though personally I think not. I understand protecting pitchers from injuries and hitters 3 times through but unless they are struggling there is no reason to take pitchers out early. Also when you bring in more pitchers you are relying on more pitchers to be on their game which is less likely the more pitchers you use. The most famous example of this philopshy change back firing is Game 6 of the 2020 World Series when Kevin Cash pulled Blake Snell after 5.1 innings and 73 pitches when he was dealing. Cash relied on more pitchers to be on their game. Unfortunately, they weren't leading to the Dodgers winnning the World Series. MLB also doesn’t like the change in starting pitchers role as there were reports recently that they may try to enforce a minimum 6 innings for starting pitchers. This could restore starting pitchers to their former glory but whether this actually occurs remains to be seen.