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Staturday: (SI[ERA)-]

Today we will continue looking at some pitching sabermetrics: ERA- and SIERA.


ERA- (Earned Run Average Minus) is just like ERA except it includes park factors and league averages and boils it down to a simple number. In a way it's like wRC+ but pitching. Here is the formula:

So all it takes is just the pitcher's ERA, the park factor, and knowing the average ERA for the league. That's it. Instead of seeing a number like 3.90 though, league average for this stat is 100 just like wRC+ or OPS+. However, ERA- is different in that anything below 100 is better than league average. Don't let it confuse you. If you see a stat with a + or - at the end of it just know that 100 is league average and the + or - symbol tells you which direction above average is. (There is also FIP- and xFIP- and they are largely the same as ERA-)


SIERA stands for Skill-Interactive Earned Run Average. What the heck does that mean? Well it is in the same family as FIP and xFIP (hopefully you remember them from last week but if not click here), but unlike the FIPs, SIERA actually looks at balls put into play. I am not going to show you the calculation for SIERA and if I'm not doing that then you know it's crazy. Instead I'm just going to highlight a few key things about the stat.


SIERA weighs strikeouts higher than FIP or xFIP. It does this because pitchers who strikeout more batters tend to give up weaker contact (the pitch is harder to square up therefore resulting in less damage done). It also will weigh a pitcher's walk rate differently. A pitcher who gives up fewer walks tends to have better control and can maintain how many men are on-base versus a pitcher with a high walk rate.


As far as balls in play, a pitcher with a high ground ball rate will tend to give up more hits in a season, but they also give their defenses a chance at turning a double play. A ground ball also usually doesn't end up as an extra base hit as often as fly balls and line drives. A similar reasoning is used for pitcher's with a high fly ball rate. They will normally have a lower HR/FB ratio than a ground ball pitcher but they most likely will give up more extra base hits. However, they may give up fewer hits since fly balls are more often turned into out than ground balls.


PHEW. That seemed like a lot to take in. Here's what you need to take away from SIERA: 1) It is a family member of the FIP family but it takes into account of balls in play. 2) It does take into account park factors. 3) It is presented just like ERA/FIP/xFIP so if you see a 2.90 versus a 3.90, you know the pitcher with a 2.90 had a better year. 4) This is one of the most comprehensive pitching stats you will probably not see while watching a baseball game, so why am I telling you about it? I think it is a useful stat and just adds another tool for you to use while evaluating players.


No more walls of text next week (scouts honor). Next week we will look at O-Swing%, Z-Swing% and other plate discipline stats. These stats can be used for both pitchers and hitters.




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