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Mound Visit: Primer on pitching metrics ☕️


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STATE COLLEGE, Pa. — In Part 1 of my advanced stats primer yesterday, I took a look at some of the more advanced ways to look at hitting. Today, let's turn our attention to the hurlers. At some point next week, we'll tackle the nebulous area of fielding stats.

Spin rate

What is it: Spin rate refers to, well, just that -- the revolutions per minute on any given pitch after it leaves a pitcher's hand. By far, the biggest advancement in pitching over the past several years has been the emphasis on this metric, and for good reason. Perhaps more than most other metrics, it can be used to describe how unique a pitcher's breaking ball can be.

For example, Kyle Crick currently carries the highest average spin rate on sliders among all MLB pitchers with a 3,197 rpm rate (minimum: 50 sliders thrown). While not the only metric that matters, the high spin rates on his sliders go a long way toward carrying a 49.4 percent whiff rate on the pitch. The higher the spin, the harder it will be for a hitter to pick it up. Crick's spin also affords him a degree of protection against balls that might sail on him a bit, as you'll see in this short but sweet highlight video:

Spin is infinitely easier to manipulate on breaking balls than on fastballs, especially those of the four-seam variety. By changing seemingly simple factors such as grip or placement of fingers, pitchers can add or reduce spin. Fastballs, on the other hand, have far less variability in spin factors. Those that do have high spin fastballs tend to see more swing and miss.

In case you were wondering, yeah, Felipe Vazquez carries the highest four-seam fastball spin rate among Pirates hurlers, with an average rate of 2,161 rpms.

In a nutshell: How a pitch spins around once it leaves the pitcher, expressed in revolutions per minute (RPM).

Use it in a sentence: Indians starter Trevor Bauer was merely treading water since he was drafted, until he began tinkering with his breaking pitches. He has been able to add 300+ RPM on average to his breaking balls since 2015, and it has turned him into a top-flight pitcher.

Strikes and walks - % vs /9

What is it: Going to cheat a little bit here and talk about the ideas of percentages vs "per nine" stats when it comes to pitcher walks and strikeouts.

You may have commonly seen pitchers carrying a K/9 or BB/9 statistic. An example would be "Pitcher X is striking out 10.5 batters per nine innings, while walking 2.3 per nine." This worked well enough until a new contender entered the ring in K% and BB%.

Simply put, X/9 extrapolates a pitchers' strikeouts or walks normalized over nine innings. It is arrived at by multiplying the number of strikeouts or walks by nine, and then dividing that number by innings pitched.

K% and BB% on the other hand, simplifies things considerably. Rather than requiring more math, these statistics boil things down to "How many batters did you walk/strikeout?" by taking the amount of strikeouts or walks and dividing it by the total number of batters faced. For example, if Felipe Vazquez struck out 66 out of 100 batters faced, he would have a 66 percent strikeout rate.

In many ways, strikeout and walk percentages are much, much better to judge relievers by because their total number of innings pitched is dwarfed in comparison to an average starting pitcher who makes at least 20 or more starts. The "per nine" stats are still being used widely to draw conclusions on starting pitchers, though that is starting to fade as starters pitch fewer innings per start.

In a nutshell: These are simply better ways to judge a reliever's ability to strike a hitter out, or limit walks.

Use it in a sentence: Padres reliever Craig Stammen is not striking out many batters -- just 18.8 percent on the year -- but is elite when it comes to limiting walks, with a season-long rate of 1.5 percent.

Whiff per swing

What is it: Whiff per swing is often confused with Whiff percentage. And why wouldn't it, as the nomenclature is very similar. Let's pay attention to the "per swing" descriptor, as this tells us that whiff per swing is the amount of swinging strikes divided by only the number of pitches a hitter swings at, not the total amount of pitches seen. So, for the Crick example above, "49.4 percent whiff rate," refers to whiff percentage, not whiffs per swing.

Whiff per swing is more useful than overall whiff as it can give us a better picture of a pitcher's ability to fool a hitter into a bad swing, rather than just looking at raw numbers.

In a nutshell: A better way to understand a pitcher's ability to get a swinging strike

Use it in a sentence: He's had a rough go of things in 2019 thus far, but Chris Archer's slider has actually reached a new level of effectiveness. His 41.67 percent whiff per swing rate on the pitch is the highest of his career.


What is it: Fielding Independent Pitching is an improvement upon Earned Run Average, The idea is to set defensive and contact rates to current league averages in order to better adjust for a "bad defense" or "bad luck" behind a pitcher. By limiting FIP to count only what a pitcher can control -- his action -- we can see a better window to his effectiveness. Much like xwOBA/wOBA, a pitcher with a higher FIP but a low ERA would be considered "lucky," with the converse being true as well.

In a nutshell: Like ERA, but better!

Use it in a sentence: In 2018, Jameson Taillon's 3.20 ERA was well earned, backed by a 3.46 FIP.

Make sure you bring your popcorn, as we'll get down to the nitty and gritty of advanced fielding stats in our next installment.

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