RADIO
This article looks at plate discipline metrics for minor league hitters including contact % and swing % to help fantasy leaguers evaluate contact and patience skills among hitting prospects.
Swing % and contact % are among the quickest, if not the quickest, metrics to stabilize for hitters. ‘Stabilization’ is a term used to indicate a metric’s reliability or its correlation with itself in the future. More stable metrics provide a more meaningful indication of a player’s talent in smaller samples.
Looking at plate discipline metrics can give you an idea of whether a hitter’s K% or BB% is sustainable or not, especially in smaller samples.
Editor's Note: Our incredible team of writers received five total writing awards and 13 award nominations by the Fantasy Sports Writers Association, tops in the industry! Congrats to all the award winners and nominees including Best MLB Series, NFL Series, NBA Writer, PGA Writer and Player Notes writer of the year. Be sure to follow their analysis, rankings and advice all year long, and win big with RotoBaller! Read More!
Gathering the Data
Though FanGraphs publishes a full suite of plate discipline metrics for major leaguers and certain metrics for minor leaguers (e.g., swinging strike %), much remains unpublished. Thanks to Bill Petti’s indispensable baseballr package for r, this data is accessible to the public, although it demands a fairly slow and painstaking collection process if you’re pulling a lot of data (Petti outlines the process here).
For this article, I have compiled a leaderboard capturing minor league data for all hitters Class A or above, with a minimum of 100 pitches seen, through Saturday’s (6/25) games. The leaderboard features:
- contact % (the percentage of total swings a hitter makes contact on, including fouls but excluding foul tips)
- swing %
- called strike %
- foul strike %
- swinging strike % (including foul tips)
- ball %
For swing %, called strike %, foul strike %, swinging strike %, and ball %, the denominator is total pitches, whereas for contact % it's total swings).
You can view the full leaderboards at Scout the Statline, a website I co-publish with Ross Jenson as a house for our various metrics and leaderboards.
I leverage past research from Mike Podhorzer and Jeff Zimmerman to develop expected K% and BB% metrics for each hitter. These metrics show a hitter’s expected K% and BB% given his contact %, swing %, called strike %, and foul strike %. Zimmerman's MLB models also capture whether a pitch was in the zone or outside the zone, but this data is not easily reproducible at the minor league level – an area for future research. I regress 2022 K% and 2022 BB% minus K% on the 2022 plate discipline metrics, a form of descriptive regression following past norms in expected hitter metrics.
Together, the four metrics explain 92% of the variance in hitter K% and 86% of the variance in hitter BB% minus K% (I train the model on n = 351 Class A Advanced hitters). I then use expected BB% minus K% and expected K% to derive an expected BB% (note: hitter BB% minus K% is a superior metric for hitters, capturing the combination of patience and contact skills, in the same way that K% minus BB% is a superior metric for pitchers). A higher contact % is associated with a lower K% and a higher (better) BB% minus K%, whereas called strikes and foul strikes are associated with worse K% and BB% minus K% outcomes. A higher Swing % is associated with a lower K%, but also a lower (worse) BB% minus K%.
Expected K% and BB% for Notable Prospects
Table note: minor league averages: 71% contact, 47% swing, 16% called strike, 17% foul strike, 14% swinging strike, 37% ball, 16% in-play strike. Averages only vary slightly from league to league and level to level.
The above table shows expected K% and BB% risers and fallers for some noteworthy top prospects. Expected K% and BB% paint a brighter picture for many top prospects, particularly Jarred Kelenic, Nolan Gorman, and Jo Adell. Adell’s 70% contact suggests he deserves better than the 33% Triple-A K% he has posted so far, and the model foresees a stronger xBB% as well. Most of his plate discipline metrics are close to Triple-A average, yet his BB% minus K% is below average – I’d bet on some gains moving forward.
I included Gunnar Henderson and Esteury Ruiz here because they are two of the biggest year-over-year improvers in terms of BB% and K%, and I was curious how “real” their improvements were. Expected BB% and K% fully validate Ruiz’s performance thus far. Henderson may deserve a slightly worse K% and BB% according to the expected metrics, but he has been so outrageously good this year that his xK% and xBB% are still elite even allowing for some decline. Similarly, many of the decliners featured above, like Royce Lewis, and James Wood, have been good enough by K% and BB% to still look good even allowing for some decline. On the other hand, Vidal Brujan’s declines are a bit worrisome, especially when paired with his elevated K% at the MLB level.
In addition to the names in the table above, a few additional names are worth mentioning on account of how good they have been in blending patience and contact abilities: Adael Amador and Jorbit Vivas. Both are among the minor league leaders in xBB% minus xK%, validating their exceptional BB% minus K% (Amador's xBB% is 13% and his xK% is 11%, while Vivas' xBB% is 13% and his xK% is 9%). Both Amador and Vivas are among the youngest players at their level, Class A and Class A Advanced, respectively, and both have shown some pop, unlike many of the other league leaders in xBB% minus xK%. Both guys have gotten a fair amount of love in prospect circles, but I'd argue they still deserve even more – both remain underappreciated.
Conclusion
This article dug deep into plate discipline metrics to better evaluate contact and patience skills for minor leaguers. I plan on producing a similar expected K% and BB% leaderboard for minor league pitchers shortly. I will also update the minor league hitters leaderboard hopefully monthly (it’s a pain or else I’d do it more frequently). When analyzing hitter patience and contact skills, don't stop at BB% and K%. Diving into plate discipline metrics can help you determine how sustainable a given BB% or K% is.
Download Our Free News & Alerts Mobile App
Like what you see? Download our updated fantasy baseball app for iPhone and Android with 24x7 player news, injury alerts, sleepers, prospects & more. All free!
More Fantasy Baseball Advice
