Beginner’s Guide to Advanced Pitching Stats


The saber metrics and advanced analytics of baseball can be very intimidating to casual fans and even some of the most passionate fans out there.  There are so many stats, many with very complex formulas, that it can keep interested individuals from ever digging deeper into this great sport.  If you are interested in gaining better understanding of some of the fundamental statistics, look no further.  Through BSS I’ll be posting three pieces that should make things more clear.  Below we will get into pitcher stats, with articles on offensive and defensive stats coming in the future. 

Photo courtesy of

Before I really get into pitching statistics I’d like to credit as they post all of this information and help create and track stats.  They are a great place to seek baseball knowledge, and I am merely trying to simplify their explanations without so many numbers and more educated phrases, as I know it is very tough to understand things when you come in without much knowledge.  All of the league averages for stats and a good chunk of my knowledge comes from them.  This is a great site to use and they could use all our support. 

Strikeout Rate (K%) and Walk Rate (BB%)

These ones are nice and simple.  K% is the percentage of hitters faced a pitcher strikes out, and BB% is the percentage of hitters that a pitcher walks.  League average strikeout rate is 20% and average walk rate is 8%. 

Fielding Independent Pitching (FIP)

FIP tries to measure a pitcher’s ERA without accounting for his specific team’s defense.  Per Fangraphs it “strips out the role of defense, luck, and sequencing, making it a more stable indicator of how a pitcher actually performed over a given period of time...”.   This stat is really useful because it isolates the pitcher’s results and gives us a better idea of how he really pitched, regardless of factors he has no control over.  League average FIP is 4.20, while really good pitchers will achieve a 3.20-3.50 and someone pitching rather poorly will have around a 4.70-5.  xFIP is another stat that basically takes FIP and goes a step further, removing some of the randomness in HR/Flyball%.

Skill-Interactive ERA (SIERA)

SIERA has become one of my favorite stats.  This stat takes into consideration the reasons a pitcher is successful or unsuccessful rather than, as Fangraphs puts it, “largely ignoring balls in play” like the other FIP/xFIP.  What does this mean?  According to SIERA, high groundball rates, average or better walk rates, and high strikeout rates are the most important stats to success.  These are the best routes for a pitcher to prevent as many runs as he can.  Fangraphs has calculated the rough league average SIERA to be 3.90. 

ERA- and FIP-

These stats, along with xFIP, consider park factors and give us player performance in comparison to the league average.  This is especially important for discussions on pitchers in bad environments like Colorado’s Coors Field.  With park adjusted stats, we can fairly compare someone in an especially pitcher-friendly or hitter-friendly park to the rest of the league.  League average ERA- and FIP- is 100 and the lower you get, the better the pitcher (Ex- Jacob Degrom’s amazing 2018 granted an ERA- of 45, and Rick Porcello’s rough 2019 resulted in a 114 ERA-). 

O-Swing% and Z-Swing%

These stats tell us plate discipline hitters have against a certain pitcher, and also gives us an idea of how nasty the movement on a pitcher’s stuff is (which can then likely be backed up with MLB Statcast data).  O-Swing% gauges the percentage of swing on pitches outside the strike zone, while Z-Swing% tracks swings on actual strikes.  We can use these to tell how aggressive or passive hitters are against a pitcher.  According to Fangraphs, the average O-Swing% and Z-Swing% are 30% and 65%, respectively. 

Thoughts on the Wins Stat

In my estimation, pitcher Wins tend to be a very overvalued statistic (especially in the Cy Young Award considerations).  The correlation between Wins and a pitcher’s actual performance isn’t all that strong.  For example, Eduardo Rodriguez had a great season but didn’t really earn the third most wins in MLB as he ranked 25th in ERA and 46th in WHIP.  This goes to show how run support and the points in a game where runs come can make wins an unfair stat to compare pitchers.  Pitchers should be judged on a range of stats that better show individual performance.  If you really need one stat to show how many games a pitcher performed well in, I’d point you to Quality Starts (# of appearances with 6+ innings pitched and 3 or less earned runs).  

This concludes my list of beginner’s advanced pitching stats.  Let me know if this helped you in the comments or on Twitter @EBolligerSports.  You can look forward to a couple other pieces like this one for defense and hitting in the near future!

Follow Evan on Twitter @EBolligerSports

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Boston Sports Syndicate: Beginner’s Guide to Advanced Pitching Stats
Beginner’s Guide to Advanced Pitching Stats
Boston Sports Syndicate
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