The MLB Postseason Effects of Regular Season Performance Against Top of the Rotation Starters

In the ensuing discussion of Review of First Half Rotation Matchup Luck, Reddit user /u/JustTrynaChill posited the question of the effect of regular season success against top-of-the-rotation starters on playoff success. This certainly was an intriguing question, and so using similar parameters, we’ll investigate the query.

To examine this effect, we’ll look at the 40 playoff teams from 2012 to 2015, the beginning of the expanded Wild Card era. During each individual season, we’ll investigate the performance of the team versus the top two quintiles of MLB starters by FIP. We’ll limit these starters to ensure that they have at least 80 IP as a starter (approximately half a season), to guarantee that they had a significant enough effect on their team’s season to qualify.

Quantifying Regular Season Success Against Top Starters

On average, a team will face a #1 or #2 starter in the league (by FIP) approximately 35-40% of the time. As we saw last week, we expect the average team to win approximately 43.5% of the total games against top-of-the-rotation starters.

Of course, we should expect a playoff team to be better than average, and they are indeed. Over the last 4 seasons, the 40 playoff teams have averaged a 49.4% winning percentage against top-of-the-rotation starters. During their playoff runs, the average playoff team of the last 4 years expected 3.5 wins against the competition. Due to the varying lengths of each round, this number is not a perfect expectation of a team’s performance, but it does indicate what the baseline performance will be. The results for all 40 teams shown below. The teams highlighted in gold won the World Series, and the teams highlighted in silver lost the World Series.


Quantifying Postseason Success Based on Regular Season Success

Using the results of each of the 40 playoff teams from 2012-2015, we will plot the regular season winning percentage against the number of playoff wins. We’ll separate the teams into 4 quadrants. The first quadrant represents teams that performed better than average during the regular season against top-of-the-rotation starters and overperformed MLB Postseason expectations. Quadrant two will represent teams that overperformed Postseason expectations despite lackluster regular season success. Quadrant three indicates teams that both underperformed regular season expectations against top-of-the-rotation starters and Postseason success. Lastly, teams in quadrant four indicate ones that underperformed playoff expectations despite performing well during the regular season.


The Best Playoff Teams Don’t Have the Best Regular Season Success Against Top Arms

As we can see, only 6 teams appear in quadrant one, the 2013 Red Sox, the 2015 Royals, the 2013 Cardinals, the 2015 Cubs, the 2014 Cardinals, and the 2013 Dodgers. These teams outpaced both average regular season against top-of-the-rotation starters and average MLB Postseason success. The 2013 Red Sox and 2015 Royals both finished the season as World Series Champions, while the 2013 Cardinals lost in the Series against the Red Sox. The other two recent World Series Champions, the 2012 and 2014 Giants, won the Series despite below average performance against top starters. Other teams that appear in quadrant two include the 2014 Royals and 2015 Mets who each lost the Series.

What is particularly telling about this graph is the line of best-fit, displayed roughly around the x-axis. With an R-squared of 0.00042 (out of 1), this indicates that there is no relationship between Regular Season success against top starters, and MLB Postseason success.

What Trade Deadline Deals for Top Arms Means

As teams spend the trade deadline trying to acquire top-of-the-rotation starters like Chris Sale, Chris Archer, Julio Teheran, Sonny Gray, Rich Hill, and others, their competition may fear the arms race. But ultimately, the only effect this has is on which teams actually make the playoffs, as Fangraphs studied last year. A team comfortably in the playoff race and not in the market for a top arm has no reason to fear the effect on its postseason, as they are just as likely as any other team to make and win a World Series appearance.

Readers, what do you think? Do teams benefit in the MLB Postseason based on how they do against top starters? Which players do you think teams will look to acquire at the trade deadline to help, and why will they help in the MLB Postseason? Leave your thoughts in the comments below or on Twitter @SaberBallBlog. Don’t forget to subscribe to SaberBallBlog by clicking the green “Follow” button in the menu, and follow on Twitter for all of the latest updates on the MLB!

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One response to “The MLB Postseason Effects of Regular Season Performance Against Top of the Rotation Starters”

  1. […] in baseball is everything, it comes up again and again in different areas of the game. One area in which it is particularly important is the batting order, and which hitters come to the […]

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