A couple of weeks ago, I looked at the ways in which you might use batted ball statistics like BABIP and home run to fly ball rate to inform your fantasy decisions. In this post, I’ll be doing the same for the range of plate discipline stats that are available to us.
As with the batted ball statistics, a variety of sources carry at least some of these, but FanGraphs is the best place to find all of them on one player page, or create a leaderboard using them.
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Strikeout rate (K%) and walk rate (BB%)
For K% and BB%, just divide the total number of strikeouts or walks by the total number of plate appearances. This is the purest way to know exactly how often a hitter or pitcher is achieving each outcome. In 2016, the league-average walk rate was 8.2%, with a strikeout rate of 21.1%.
Why do we care about how often players achieve these outcomes? Fundamentally, every strikeout is a ball that isn’t being put in play. As discussed in the previous post, while players can exert some control over this, there is a lot of random variation, especially for pitchers. A pitcher like Max Scherzer, who struck out almost a third of all batters he faced last year, is much less subject to batted ball luck than the league average pitcher. Even if it’s an out, a batted ball can still advance a runner, and frequently it will be a hit, perhaps even a home run. Strikeouts have none of these issues and are one of the more reliable fantasy statistics on a year-to-year basis. Walks are naturally bad for the obvious reason that it’s an extra player on base who can score.
For hitters, every strikeout is another at-bat taken away that hurts their batting average and another lost opportunity for a run, home run or RBI. It’s also very difficult to strike out a lot and record a high average. No hitter ever strikes out 30% of the time and also hits .300. Hitters who walk a lot tend to be less volatile in terms of their fantasy production, because even in a stretch of bad BABIP luck they still get on base, and they are usually more selective about which pitches they swing at, making it less easy for pitchers to get them out. In OBP leagues, there is obviously a direct link between BB% and fantasy production.
These are also two important statistics to be aware of because they are very quick to stabilize compared to most numbers. Baseball Prospectus writer Russell Carleton has shown that strikeout rate and walk rate are among the statistics which require the fewest plate appearances to become reliable: around 60 PA for K% and 120 PA for BB%. As Carleton puts it, these are the points at which “the rate of signal to noise crosses the halfway point”, and therefore it’s reasonable to assume these numbers are decent measures of a player’s true talent.
Of course, talent levels and circumstances can change, and there are so many variables that go into performance that it’s a mistake to say that this means we know what a player’s actual performance level will be going forward with any high degree of certainty. However, of all the numbers we have available to examine for players, these are two that should be at the top of the list in terms of reliability, even with a relatively small sample size.
Strikeouts per nine (K/9), walks per nine (BB/9) and strikeout-to-walk ratio (K/BB)
On the pitching side, you may also be familiar with strikeouts per nine (K/9), walks per nine (BB/9) and strikeout:walk ratio (K/BB). While K/9, BB/9 and K/BB are often cited, these have their limitations. Pitchers who walk a lot of batters and give up a lot of hits can achieve good K/9 numbers because they simply face more batters.
A pitcher who gives up two hits, two walks and strikes out one, with a double play, will have the same K/9 as a pitcher who gets two groundouts and a strikeout, but the latter is clearly much more valuable. With K%, the first pitcher would have a 20% rate, and the second would have a 33.3% rate.
Francisco Liriano is a good example: last year he ranked 13th for K/9 amongst qualified starters, but 22nd in K%, given his high walk rate and the fact that he gave up almost a hit per inning. The K/9 number alone would give you the impression that he was much more successful, but as an inning is not a set number of batters, it’s not actually an effective way to tell how often he is successful.
K/BB also can be particularly misleading with regard to pitchers who do not walk anyone. Josh Tomlin was second in K/BB last year but that was because of his miniscule 2.8% walk rate. If we use strikeout rate minus walk rate (K%-BB%), we can see that Tomlin was actually 39th amongst qualified starters, a mark much closer to what his 4.40 ERA might suggest.
That isn’t to say that the per nine stats aren’t useful, because you can still get a fairly clear idea of how good a player is from a quick glance at their K/9, BB/9 and K/BB and they are easier to translate into raw numbers as we’re used to thinking about pitchers in terms of innings. However, in terms of comparing the actual quality of pitchers, the percentage stats are more accurate indicators.
What if we want to dig deeper into a player’s profile and find out exactly how they’re arriving at their walk and strikeout rates? That brings us to a further set of statistics.
Swings, Contact and Zone Percentages
If we really want to know whether a hitter is good at leaving pitches he can’t hit, or a pitcher is great at making hitters chase, this collection of stats is a great place to start. Swing% and Contact% simply give the overall percentage of pitches swung at and the percentage of those swings on which contact was made. Zone% tells us how often pitches were in the strike zone. Swing% and Contact% are then further broken down by whether they were in (with the prefix Z-) or out (O-) of the zone.
You’ll also notice that these stats are repeated with slightly different numbers. They appear first under ‘Plate Discipline’ on the FanGraphs player page, but then also under ‘PITCHf/x.’ The first set are based on Baseball Info Solutions data but have been modified by human checkers. The second are simply pulled straight from the PITCHf/x pitch tracking system. The two will be broadly in agreement, but there will be some differences based on the interpretation of the strike zone. Here are the league averages by each set of data for 2016:
| Stat | BIS | PITCHf/x |
| O-Swing% | 30.30% | 30.60% |
| Z-Swing% | 66.70% | 63.90% |
| Swing% | 46.50% | 46.50% |
| O-Contact% | 63.90% | 62.10% |
| Z-Contact% | 86.30% | 86.50% |
| Contact% | 78.20% | 78.10% |
| Zone% | 44.60% | 47.80% |
To take some examples of hitters at the extremes, Dexter Fowler had a 19.4% O-Swing% last year, meaning he swung at fewer than 1 in every 5 pitches outside the zone, the lowest percentage among qualified hitters. Jose Iglesias had a league-leading 96.9% Z-Contact%, showing that he made contact with almost every pitch that he swung on when it was in the zone.
Hitters who swing outside the zone a lot can succeed, but they usually need excellent bat control, or to be selective enough to recognize the pitches that they can still barrel. Adam Jones has made a career out of being aggressive, sometimes swinging at more than 60% of pitches and over 40% of balls. He swings and misses a lot, but makes very hard contact when he connects. Just don’t expect hitters like Jones to walk a lot.
Much like the batted ball stats, there isn’t an ideal profile that guarantees success, but again there are things we can look for that might suggest improvement or future struggles, as well as telling us how a pitcher is succeeding or failing. For instance, Z-Contact% for pitchers can show who has the ability to blow the ball by hitters or simply deceive them so effectively that they can throw the pitch in a hittable spot and still not get hit. The pitchers with the lowest Z-Contact% in 2016 were either those with elite velocity and/or stuff, such as Scherzer and Clayton Kershaw, or those with notably deceptive components in their arsenal, such as knuckleballers Steven Wright & R.A. Dickey.
Once again, it’s crucial to incorporate other elements into the analysis, as Dickey’s presence there shows. Just because he has a pitch that’s sometimes extremely difficult to square up, it doesn’t mean that he’ll be an effective pitcher overall. Similarly, pitchers with great stuff who don’t know how to sequence, don’t have enough deception, or can’t throw a strike when they need to might be able to fool lesser hitters and have impressive contact numbers overall, but will be found out against those with a better approach.
First Strikes and Swinging Strikes
First strike percentage (F-Strike%) is another useful tool in this regard, as it shows pitchers who fall behind in the count early and often. This can be a bad sign for pitchers, as they are frequently forced to throw pitches in the zone to catch up and therefore surrender the advantage to the hitter. It can often limit a pitcher’s ability to go deep into the game as they start many at-bats by falling behind 1-0 and will have more pitches per plate appearance.
League average for F-Strike% in 2016 was 60.3%, with the highest mark close to 70% and the lowest in the low-50s. F-Strike% can also be reflective of the way that pitchers are attacking hitters, or if they’re keen to avoid attacking them at all. A lot of game theory is involved with pitch selection, location and sequencing, so first strike strategies can vary based on numerous factors, such as how likely the player is to swing at the first pitch and how their approach changes when they are behind in the count.
It also means that there’s a balance to be struck. Pitchers don’t want to be behind in the count, but if they become too predictable and always throw first-pitch strikes, hitters will start teeing off on them. Of course, sometimes a low F-Strike% is simply due to the fact that the pitcher can’t throw strikes every time they want to, which is why Liriano and Carlos Rodon were among the worst pitchers for this in 2016.
That brings us to the last aspect of plate discipline data; swinging strike rate (SwStk%). This is the percentage of total pitches that are swinging strikes. The league average last year was 10.1%, with starters at 9.5% and relievers at 11.1%.
It is impossible to fake swinging strike rate over any sort of decent sample. Batters might swing and miss more often against pitchers they haven’t seen before, but only those with true strikeout stuff will put up a good SwStk% over a longer period of time.
If you see a pitcher with high strikeout numbers but below average SwStk%, it’s likely that they’ve not been fooling hitters as often as the raw numbers suggest, and their rate will come down in the future. Pitchers who can sustain decent strikeout totals without having great swinging strike rates tend to be those who can get ahead in the count, have excellent command and control, and can throw multiple pitches exactly when they need them, such as Jose Quintana. Similarly, a high SwStk% without the strikeout totals to go with it could suggest some positive regression, or a pitcher who needs to change their approach to better utilize their repertoire.
The top of the SwStk% leaderboard tends to be a who’s who of elite pitchers – Kershaw, Scherzer, Noah Syndergaard. Every now and then you will also find a pitcher, frequently younger, who has yet to turn their arsenal into the production you might expect. Michael Pineda and Robbie Ray are prime examples of this. Sometimes those pitchers never develop the consistency or the approach they need to truly break out, but at the very least they should record very useful strikeout numbers for fantasy.
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Darius Austin is a correspondent at FantasyPros. For more from Darius, find his work at Friends with Fantasy Benefits, BP Wrigleyville, Banished to the Pen and Bat Flips & Nerds and follow him @DariusA64.
