Relievers and the Growth of Strikeouts

Dellin Betances set a strikeout record on Saturday:

Yankees RHP Dellin Betances on Saturday became the first pitcher in Major League history to strike out at least 100 batters as a reliever in five straight seasons.

I doubt he will be the last. Over time, more and more strikeouts are being pushed into the bullpen. This spreadsheet tries to display what happened over the last 60 years. In the late 1950s, starting pitchers faced about 71% of batters, but recorded about 70% of strikeouts. Even then, relief pitchers were slightly better at striking out batters than starters. The percent of batters faced by starters shrunk over time, down to 61% this season after a rapid five-year drop. The gap between percentage of batters faced and percentage of strikeouts recorded by starters has widened to about three points. Relievers continue to strikeout batters more often than starters, and the gap is widening despite less work by starters. See the graph labeled Pct Starters BF and K.

A second chart shows this same concept a bit differently. It looks at the share of strikeouts per 1000 batters faced. In 1957, batters struck out about 125 times per 1000 PA. Eight seven of those came from the starters, 38 from relievers. In 2018, batters strikeout about 221 times per 1000 PA. One hundred thirty of those come from the starter, 91 come from relievers. The share of strikeouts by relievers more than doubled, while the share of strikeouts by starters is up about 50%.

Note in the chart labeled Strikeout per 1000 Total Batters the recent history of the increases. Between 2007 and 2010 inclusive, starters went from 104 K per 1000 total batters to 118. The relievers then followed, going from 77 in 2015 to 91 today. I believe 2015 was the year the Royals convinced the rest of baseball that fire balling relievers led to championships. Enjoy the data.

from baseballmusings.com https://ift.tt/2PuwyjN