Ryan Pressly is the Best Reliever in Baseball Since Joining the Astros.

Yesterday the Hebrew Hammah argued that Roberto Osuna is the best reliever in baseball this year. Today I will use my extensive French vocabulary to proclaim: au contraire. It’s our other great relief pitcher, Ryan Pressly, who is the best reliever in baseball, at least since his arrival in Houston.

First, let’s look at this season. Here are the top relief pitchers in baseball as of April 17th, 2019 by FIP, xFIP, xwOBA and WHIP. I threw in their ERA’s and K% just for a look but I used the other four measures to judge who deserved to be in the “best of” category.

Based on these statistics from a very small sample seven relief pitchers stand out this year so far. They are, rookie Nick Burdi, in the top four in FIP, xFIP, SIERA, and xwOBA, another rookie, Nick Anderson, in the top seven in FIP, xFIP, and SIERA, Ty Buttrey, in the top two in FIP, xFIP and SIERA, Matt Barnes, in the top four in FIP, xFIP, and SIERA, and Edwin Diaz, in the top six in xFIP and SIERA. I must not forget Hammah’s favorite, Roberto Osuna, first in xwOBA and WHIP.

But now I make the case for my guy, Pressly, who doesn’t occupy first in any one category, but is in the top five in all of them, and number three in WHIP. Unlike some of the others on this list he has not surrendered a run, not surprisingly since he has not surrendered a walk and only three hits in almost eight innings.

OK, so according to the advanced metrics like SIERA and xwWOBA, which are intended to evaluate how well a pitcher is pitching with luck factored out, and predict his future performance based on present contact data, Pressly is only in the top five. However, that is top five in every advanced category, and the difference between one and five in SIERA, Fangraph’s favorite pitching metric, is negligible.

But when you combine Pressly’s high scores in the advanced metrics with his success in actual results, keeping runners off the bases, (WHIP) and keeping runs from scoring, (ERA) the things relief pitchers are hired to accomplish, I think he has been the best and most well-rounded overall reliever in baseball this year.

Of course after only about one tenth of the season it is premature to speculate about who is the best reliever in baseball so far, especially since two of the contenders, Nick Burdi and Nick Anderson are rookies

The subject of this essay is a little broader: who is the best reliever in baseball since Ryan Pressly joined the Astros last August. It’s a close call, but I say Pressly. Here’s why.

This is my methodology. To determine who deserves consideration as best relief pitcher since last August 5th, Pressly’s debut, I took the 10 best relievers in the following categories: FIP, xFIP, SIERA, WHIP and xwOBA. I also included the aforementioned top performers in 2019 except for those with less than 10 career innings. I then compiled their performances in these areas since August 5th, 2018, the day of Pressly’s Houston debut. These are the pitchers, besides Pressly, who made the intial cut.

Edwin Diaz..........1.06 SIERA Josh Hader..........1.78 SIERA

Dellin Betances..2.03 SIERA Kirby Yates..........1.62 SIERA

Corey Knebel.....1.62 SIERA Brad Peacock.....3.05 SIERA

Blake Treinen.....2.70 SIERA Will Smith...........3.35 SIERA

A. Chapman.......3.46 SIERA Will Harris............3.46 SIERA

Ty Buttrey...........2.15 SIERA Matt Barnes........2.32 SIERA

Roberto Osuna..3.10 SIERA Lou Trivino..........3.52 SIERA

Sean Doolittle....3.10 SIERA Adam Ottavino....3.61 SIERA

Jose Castillo.......2.37 SIERA

The following chart allows us to compare Pressly with these pitchers. For the sake of simplicity only those pitchers with an xFIP or SIERA under three are included on the chart. The statistic xwOBA is not included on this chart because I cannot add the statistics across seasons.

*Corey Knebel is injured for 2019.

The best pitcher in this list according to the peripheral statistics was Edwin Diaz , whose xFIP is about .3 below Pressly’s, and whose SIERA is about .4 lower. According to these statistics, if present performance holds, we should expect Diaz to end up with an ERA somewhere around 1.20 and Pressly around 1.50. Both of these results would be amazing over an entire season, and these two pitchers project the best based on the peripherals of all the pitchers in the league. Yes, that means you Josh Hader, Blake Treinen, Aroldis Chapman, Dellin Betances et al.

But let’s look at actual performance. Ryan Pressly has the lowest ERA at 0.31, by far the best in this group. That is because in 28.2 innings he has allowed only one run, 13 hits, 3 walks and no home runs. His WHIP is by far the best in this group, meaning he has given up the fewest base runners, exactly what a good reliever is supposed to do, and he hasn’t allowed any homers to get those few base runners in. Diaz has allowed four homers, which xFIP discounts as bad luck, thus the lower xFIP for Diaz, but is it really just a matter of luck? Or has Pressly been an extraordinarily disciplined pitcher since joining Houston.

Blake Treinen’s performance in terms of WHIP and ERA are close to Pressly’s, but his peripherals are over a run worse, projecting him over time to pitch near the 3.00 ERA level.

So, even though advanced metrics give a slight edge to Edwin Diaz over Pressly, when that is balanced with Pressly’s amazing advantage in actual performance since August 5th, 2018, I believe the Astros have the best reliever in baseball, if only by a hair. And with Roberto Osuna pitching right after him, they probably have as good a set-up closer combination as any in baseball.