xERA:The Lost Metric

Imagine working on something so hard for months and possibly years, only to have unveiled at a time when no one is paying attention.

As most of you probably know by now, I am a pretty big “stats nerd” and spend a lot of my time in the Nerd Cave, compiling and comparing MLB players (especially Pirates) based on every advanced metric that is available. Now don’t get me wrong, I still like the old reliable slash line (AVG/OBP/SLG) for batters and the ERA for pitchers. I will even find myself flipping through DRS in comparing fielders’ abilities. However, there is just something about the new stats that just gets me all excited. This year OAA (Outs Above Average) for Infielders was introduced and I got lost in the numbers. The same thing happened when the JUMP stat was introduced for outfielders. I even wrote an article at the time that compared Bryan Reynolds and Starling Marte, utilizing this as one of the main statistics. So, much to my excitement when the newest advanced metric arrived earlier this week I drove in head first; unfortunately so far it feels like I am the only one.

By a show of hands, how many of you even knew there was a brand new metric to judge pitchers’ skill level? If you raised your hand you are either a lier or as nerdy as me. Everyone here has probably heard of FIP (Fielding Independent Pitching). Even Mitch Keller discovered it on his own toward the end of last season, so you probably have to. It is a pitching metric that attempts to remove “luck” and defense from the equation in order to determine how a successful a pitcher should be based on the variables that the pitcher can control; including strikeouts, walks, hit by pitches and home runs. FIP is a stat that I have fallen in love with, but even I understand that it has its limitations. It is not the be-all end-all to judging a pitcher’s performance capabilities. It can however show that there is room for improvement or at least hope. Take the previously mentioned Mitch Keller, whose “bad luck” has been written about in multiple articles. Keller had a ERA of 7.13, but a FIP of 3.19; which means that he shouldn’t have given up as many runs as he did. It doesn’t change the bottom line, the runs were scored. That isn’t the point though; I am not here to sell you on the importance of advanced metrics. I just want to open you up to the possibilities.

So, about this new metric; it’s called xERA and it’s as simple as it sounds. xERA is the expected ERA of a pitcher over time. I know that xERA itself isn’t something totally new. However, it is something that is new to Statcast and in particular Baseball Savant. The xERA in this case is based off of a pitchers xwOBA (Expected Weighted On Base Average). xwOBA, much like FIP removes defense from the equation; relying more on the exits velocity and launch angle that is produced. Sprint Speed is the last part of the equation because as we all known a faster player is more likely to get an infield hit on a high chopper to the 3rd Basemen or Shortstop, than a slow player.

With all this being said, I bet you are all wondering how the Pirates pitcher fared using this “new” advanced metric. It should come as no surprise that Joe Musgrove rated the highest/best among all qualified Pirates with an xERA of 4.08, which is .36 points better than his actual ERA. This shows the potential or expectation for improvement, but unfortunate for the Pirates and Pirates fans, Musgrove’s 4.08 xERA ranked 83rd. This ranking is a little misleading because it also includes relief pitchers. However, after a quick count, he would rank somewhere around 35 for starting pitchers; right in between John Means of the Orioles and Aaron Nola of the Phillies, both of whom had lower ERA’s than Big Joe. Long story short Big Joe is a solid starting pitcher, with potential to improve.

Some of the other Pirates starting pitchers listed include: Mitch Keller (7.13 ERA vs. 4.35 xERA), Steven Brault (5.16 ERA vs. 5.19 xERA), Trevor Williams (5.38 ERA vs. 5.30 xERA) and Chris Archer (5.19 ERA vs. 5.44 xERA). None of these make me exceptionally optimistic outside of Keller. However, this was last year and there is always room for improvement. My real concern comes when I started to focus on qualified relief pitchers. The top Pirate reliever is no longer on the team (Francisco Liriano) and the next one is currently injured (Clay Holmes). However, the delay in the season could allow Holmes to recover from his foot injury. I also don’t want to overlook the fact that the Pirates have other quality relievers that were unable to be considered qualified because of a lack of opportunities. These opportunities were limited due to either experience or injury. Keone Kela performed well in “limited” innings to the tune of a 2.12 ERA. His xERA did not fare as well and landed at 3.31. Michael Feliz is a Pirates reliever that I have been pretty high on this off-season and he did not disappoint according to this new metric, earning a 3.80 xERA versus a 3.99 ERA.

Once again I don’t want anyone to think that this metric is not without its flaws. It is just another tool that can be used in evaluating and possibly projecting future performance/value of each of the Pirates pitchers, starters and relievers.

Published by Craig W. Toth

Former Contributing Author at InsidethePirates.com, Co-Host of the Bucs in the Basement Podcast and life-long/diehard Pittsburgh Pirates Fan!

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