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5 Underlying Stats to Know (Fantasy Baseball)

Apr 11, 2019

Every year, more and more underlying statistics enter the baseball realm, and that has certainly trickled down to fantasy baseball as well. By better understanding the underlying statistics behind a player’s on-the-field performance, fantasy owners can dig deeper and get a better handle on which of their players are getting lucky or unlucky. This then allows owners to capitalize on opportunities to buy low and sell high with a higher probability of positive return on investment.

For those just beginning to dig into the numbers, here are a few suggestions from our writers on good places to start.

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What one underlying player stat should fantasy owners take note of?

xwOBA
“As far as I’m aware, you can only find xwOBA on Baseball Savant’s expected stats leaderboard. It is the golden standard for underlying metrics as far as I’m concerned. Essentially, it takes the quality of contact (exit velocity and launch angle) to determine what stats that type of contact tends to provide. A lineout to the warning track, for instance, tends to provide a double much more often than an out, so xwOBA rewards hitters with that knowledge. It then adds up all batted ball events combined with strikeouts and walks to calculate what a batter’s true hitting performance has been. We can measure luck from this since even a 500 PA sample size is not enough to see the true value of a hitter from his actual stats (BA/OBP/SLG/OPS). xwOBA has a higher correlation with future performance than wOBA does, as you might expect.”
– Bobby Sylvester (@bobbyfantasypro)

K-BB%
“In fantasy, we are obsessed with finding guys who can post strikeout rates in the mid-20s (or higher) who also have a decent WHIP. Enter K-BB rate. This underlying stat is straightforward — it is the difference of strikeout rate less walk rate. This stat helps predict future success independent of “luck” stats such as BABIP and strand rate. While this rate requires a little research (is the K-BB rate high because of super high strikeouts, super low walks, or being slightly above average in both?), it quickly tells you which pitchers are able to cast their dominance on a consistent basis. An above average K-BB rate is typically any rate in the 20s. Of course, you’ll see guys like Blake Snell post a 34% K-BB rate over his first three starts, which is the cream of the crop. Justin Verlander led all of baseball with a 30.4% K-BB rate in 2018. This stat can be found on Fangraphs.”
– Carmen Maiorano (@cmaiorano3)

BABIP
“There are a lot of advanced stats to help identify the value of a hitter, but BABIP (batting average on balls in play) continues to be uniquely predictive. While not as sexy a stat as some other sabermetric data points, BABIP remains one of the most useful metrics based on its ability to qualify luck. League average BABIP is generally around .300. Anything significantly above or below that number constitutes unsustainable luck due for regression or terrible misfortune likely to rebound. BABIP can help determine if a “hot bat” is actually crushing it at the plate or just getting absurdly lucky. This makes it easier to identify which players are draft day values or potential busts based on last year’s fortune (or misfortune), which surging hitters are worth an add off the wire, and which batters could potentially be acquired in a “buy-low” trade from frustrated owners fed up with bad luck-driven performance. A great example of this is Manny Machado, who suffered a down season in 2017 (.259/.310/.471) largely due to a horribly unlucky .265 BABIP. Shrewd drafters were able to snag Machado at the end of the second or early third round and watch his BABIP normalize (.308), which allowed him to return first-round value in 2018 with a slash line of .297/.367/.538.”
– Paul Ghiglieri (@FantasyGhigs)

Barrels
“Baseball Savant offers a treasure trove of batted-ball metrics for fantasy managers to implement. While it’s still far too early to get a definitive read on most stats, it helps to see which hitters and pitchers are making and limiting strong contact, respectively. Exit velocity and launch angle don’t always tell the full story on their own — some guys pummel the ball right into the ground, and others are only elevating harmless pop-ups. That’s the beauty of barrels, which are achieved with an exit velocity of at least 98 mph and a range of launch angle dependent on the hit speed. Balls hit high and hard naturally have a higher probability to inflict damage. Managers should take notice when a hot starter like Dansby Swanson or Daniel Vogelbach has already achieved multiple barrels.”
– Andrew Gould (@andrewgould4)

SIERA
“Moving to the mound, SIERA is similar for pitchers to what BABIP is for hitters. SIERA (Skill-Interactive ERA) measures what a pitcher’s ERA actually “should be.” Unlike previous ERA estimators such as FIP and xFIP, SIERA doesn’t ignore balls in play in favor of just strikeouts, walks, and home runs allowed. Thus, it’s more accurate and predictive, and it can clearly reveal which pitchers are over or underperforming their peripherals to tell you whether a hurler has been lucky or unlucky. Most importantly, it reveals how and why a pitcher has been successful (or unsuccessful) when it comes to preventing runs and limiting hits. An average SIERA hovers around 3.90, while anything under 3.25 is great and anything over 4.50 is poor. An illustration of this can be seen with Luis Castillo, who sported a bloated 4.30 ERA in 2018 despite a 3.85 SIERA that suggested he actually pitched much better overall than his ERA indicated. Those who traded for Castillo after his brutal start or picked him up off waivers after frustrated owners dropped him were rewarded when his numbers began to normalize, and he posted a 2.63 ERA, 1.01 WHIP, and near 25% K-rate in the second half. ”
– Paul Ghiglieri (@FantasyGhigs)

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