Strike Zone Rate Analysis - Starting Pitchers

Jon Anderson dives into strike zone rate metrics for starting pitchers to find undervalued and overvalued fantasy baseball SP for the 2021 season.

There are hundreds of metrics out there that describe pitchers. The richness of the available data is rivaled by no other sport. This can at times lead to information overload, leading us too far away from the core tenants of what success looks like. One group of statistics that are very simple and very helpful in evaluating pitchers are the "plate discipline" metrics that you can find on various websites now but were first popularized by FanGraphs.

In this post, I just want to take a really simple look at the last few years of pitcher data. It is really tough to have success as a pitcher when you cannot consistently throw strikes. I took all of the individual pitcher seasons, filtered out all pitchers who did not reach 500 pitches in a given year, and then sorted them by strike rate. This is the percent of a pitcher's offerings that end up in the strike zone (regardless of what happens with hitter contact, it is just about the location of the pitch).

Here are the top-10 starting pitchers by how often they threw the ball in the strike zone over the last four seasons.

Strike Rate Leaders (2017-2020)

Overall this is a list of very good pitchers, with some of the best pitchers in the league showing up here. Of course, this has more to do with the stuff and the confidence these pitchers have. It is certainly not true that if any pitcher just threw 70% strikes they would get Cy Young votes.

One thing I find very interesting is to see how different statistical categories correlate with each other. I did this with strike rate, here are the resulting coefficients:

Correlation with Strike%

No strong correlations here at all. The only one that meets the "significant" threshold is walk rate, which makes sense since throwing strikes a lot is the definition of how to avoid walks, although it is interesting that correlation there is as low as it is (a strong correlation will be much closer to -1 or 1 than to zero). Here is that relationship visualized:

You can see from the correlation table that throwing a lot of strikes has no positive or negative effect on your ERA, strikeout rate, or batting average against. Not a very useful statistic by itself.

Taking it a step further, we can also look at what pitchers get the most swings-and-misses on pitches they have thrown in the strike zone. The best result a pitcher can come out with is a strikeout, because it all but eliminates any chance of the batter reaching base (save the very rare dropped third strike where the batter reaches first). The way to get strikeouts is, of course, to throw strikes that are hard to hit. Reason would suggest that the pitchers that most often get whiffs on their strikes will rise to the top of the league.

Let's check that theory; here are the top-10 pitchers in "Z-Contact%", which is the percentage of the time that a hitter makes contact on a swing on a pitch thrown in the strike zone against a pitcher.

Z-Contact% Leaders, Individual Seasons, Last Four Years

The theory checks out.

However, not all Z-Contact% is created equal. If a guy gets 70% contact on pitches thrown in the strike zone, but only 30% of his pitches end up in the strike zone, that 70% does not help out very much. What we are really looking for our pitchers that stand out in both strike rate and zone contact rate.

Those pitchers will be located in the top-left quadrant of the relationship between these two categories, here:

Lots of pitches in the zone and not a lot of contact allowed on them is the name of the game here. There are 133 pitchers in that box, most of them being relievers. The fantasy-relevant starters for 2021 that are in that box are:

Yu Darvish (2020), Max Scherzer (2017, 2018, 2019, 2020), Jacob deGrom (2017, 2018, 2019, 2020), Justin Verlander (2019), Chris Sale (2018, 2019), Kevin Gausman (2019, 2020), Gerrit Cole (2018, 2019, 2020), Aaron Nola (2018), Corbin Burnes (2018), Jordan Montgomery (2020), Lucas Giolito (2019, 2020), (Brendan McKay (2019), Kenta Maeda (2019), John Means (2020), Luis Castillo (2018), Mike Minor (2020)

Choosing a 65% strike rate and an 82% z-contact rate to make our list is admittedly a bit arbitrary. Pitchers like Walker Buehler, Noah Syndergaard, Stephen Strasburg, and Corey Kluber all narrowly missed.

While this has been enjoyable thus far, no real fantasy advice for 2021 has been given yet since I have mostly rattled off a list of names that you already really wanted on your fantasy teams. Taking another look at the numbers, here are some names that might be more interesting for the purposes of the 2021 fantasy season.

Chris Paddack: In his rookie year he posted a very strong combination of 69.6% strikes and 83.7% Z-Contact%, but that faltered a bit in 2020 as he threw fewer strikes at 65.2%, but the Z-Contact% got a little better at 83.0%. He had a pretty disappointing sophomore season, which could lead to him being pretty undervalued for the upside he provides given how many strikes he throws and the quality of his stuff.

Jose Berrios: He has bounced back and forth in these categories, posting a really strong 67.5% strike rate in 2019 but giving up a good amount of contact (85.5%), and then those numbers flip-flopped in 2020 with a lower 63.5% strike rate and an 82.2% zone contact rate. If he can combine those good outcomes he could be in for a really nice season with the Twins.

Zack Wheeler: The strikeouts fell off a cliff for Wheeler in 2020 which will send his draft stock plummeting, but in 2019 he threw a ton of strikes (67.1%) and teamed that with a very good but not elite 85.1% zone contact rate. He seems to at least have the ability to put together a really good season, and he should be pretty cheap in 2021.

Lucas Giolito: He is already a well-known commodity in the fantasy world, and will likely be drafted as an SP1 this year, but it needs to be said how good his contact numbers are. He has posted marks of 77.3% and 74.6% in zone contact rate the last two seasons, elite numbers.

Sixto Sanchez: The industry will likely be very excited about drafting Sanchez in 2021, and for good reason. He threw strikes at a really high rate, especially for a rookie (67.4%), and limited contact well on those pitches (83.1%). If you are going to pay up for the uncertainty of a second-year player, this is the profile to look for.

Shane Bieber: This is actually going the other way, as Bieber does not grade out well in this study. In his Cy Young 2020 season, he was pretty mediocre in this area, throwing strikes 63.4% of the time and giving up contact on 84.4% of his pitches thrown in the zone. He was really reliant on the chase last year.

Dylan Cease: Another negative story here, Cease really does not throw many strikes (57.7% last year), and hitters do not have much trouble making contact (84.6%). That big-time fastball has really not generated great results for him.

Cristian Javier: The young Astros' starter had a really strong rookie season, but this study shows some doubt that he can replicate it (61.4% strikes, 86.3% contact).

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