Joe Nicholson-USA TODAY Sports
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April’s Most Dominant Relief Pitchers

In a field that is currently driven by advanced analytics, there seems to be a void in how we analyze the effectiveness of relief pitchers. Quite often we use starting pitcher stats such as ERA and WHIP to judge a pitcher that is put to use for a fraction of the innings. This leaves the relief pitcher vulnerable to outlier innings that inflate their overall stats and thus perception. To fill this void I developed a metric called “shutdown percentage” that tracks a reliever’s success rate in regards to dominating their outing. Before completely diving into the weeds here are a few examples of scenarios in which ERA and WHIP are ineffective evaluation tools for relievers.

Scenario 1 (ERA)

A reliever walks the bases loaded and strikes out the side. On paper, this is a fine outing as his ERA is 0.00 and he notched 3K’s. But this pitcher was far from dominant as he worked himself into a jam and inflated the overall pressure of the inning. This pressure is, however, reflected in the 3.00 WHIP he accrued for the inning. But a deeper dive into WHIP shows that it also has its blind spots.

Scenario 2 (WHIP)

A reliever pitches 3 innings in 3 consecutive games. In the first 2 games, he gave up no walks or hits. In the third game, however, he walks two batters and gives up 4 hits. His WHIP for the 3 games is now a whopping 2.00. When passing judgment on this reliever, the weight of one horrible outing overshadows the dominance of the previous two.

Why SD% Works

Quite often we are hypnotized by the 103 mph fastball and the wipeout slider today’s relievers possess. This can blind fans to the overall dominance of a pitcher. SD% asks one simple question… Did the reliever just get out of the inning, or did he dominate it? For the past 3 seasons, I have been tracking, inning by inning, each reliever’s dominance, and the results are astonishing. For this season I will be sharing these results as they unfold to determine who the most dominant relievers in baseball are. Here is a quick example of the stat in practice followed by rankings for the month of April.


Matt Foster (CWS)

April Stats: 1-1 W-L/11.05 ERA/ 1.50 WHIP

Dominant Innings 4.66

Total Innings Pitched: 7.33

SD% = 63.57%

MLB League Average 2018-2019: 54.80%

(With SD% Matt Foster is not punished for an inning in which he got lit up for 5 runs)


*Minimum 7 IP to Qualify (Minimum will augment monthly by a number TBD)

Top 10 SD% Leaders through April 30th

Team SD% Rankings through April 30th 


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Written by Nick Anton

So this, my friends, is deliciously redundant. - John Spencer