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Using Sabermetrics For Fantasy Baseball Part 5 - Plate Discipline

No matter how high a particular player's BABIP may be, his average will be mediocre at best if he strikes out too much. This is why fantasy owners have known for years that players like Chris Davis are potential drains on a fantasy team's batting average. Furthermore, players that whiff a lot tend to continue to do so - it is a very sticky trait.

In 2018, the league average K% was 22.3%, meaning that roughly one in five MLB PAs ended in a whiff. Players that K significantly less than this have an advantage in hitting for a higher average. Players that whiff more often tend to post lower averages. This is relatively common knowledge for most fantasy owners.

Let's learn how analyzing stats related to plate discipline can help improve the performance of your fantasy baseball team entering the 2019 season.

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How to Interpret Plate Discipline

Sabermetrics may be used to determine whether a given player "deserved" his K% over a particular period, avoiding misleading data the same way BABIP is used to see through a fluky average. The first number to check is SwStr%, alternatively called whiff rate. This metric simply tracks what percentage of a batter's swings fail to make contact with a pitch. The league average was 10.7% in 2018, with higher numbers indicating a proneness to K.

SwStr% tends to increase if a batter swings harder, making power hitters more susceptible to the strikeout than other players. If a player improves his strikeout rate without a corresponding improvement in SwStr%, the improvement is unlikely to stick moving forward. Likewise, a career-worst strikeout rate backed by a normal SwStr% is likely to regress in the player's favor.

Further detail is offered by O-Swing%, a measure of how often a batter swings at a pitch outside of the strike zone. Generally, swinging at pitches outside of the zone is a bad idea. Batters usually want to hit "their pitch," which they never get to see if they pop-up a fastball over their head early in the count. In 2018, the league averaged an O-Swing% of 30.9%. Numbers significantly higher than this indicate an increased likelihood of chasing a bad pitch and making poor contact or striking out.

This stat is also used to examine a player's walk rate, or BB%, in much the same manner as SwStr% is used to double check K%. A strong walk rate when a player is still chasing too many pitches is not based in any repeatable skill, and will likely be normalized moving forward. Likewise, a lower walk rate paired with a career average O-Swing% indicates that the walks should come back.

Fantasy owners should always care about walks even if their format does not directly reward them. Every BB is a chance to steal a base or score a run, and players that know the zone tend to hit for higher averages to boot!


Evaluating Players Through Plate Discipline

Let's look at some examples of advanced plate discipline stats in action. Joey Votto is widely regarded as the master of plate discipline, and his surface stats support the assessment. His 17.3% BB% was actually greater than his 16.2% K% last year, after all. Digging deeper, we find that these numbers are completely justifiable. His 16.4% O-Swing% was nearly 15 percentage points better than the league average rate, and his 6% SwStr% was roughly half the average as well. It is safe to conclude that Votto will continue to demonstrate outstanding plate discipline in 2019.

Kansas City's Adalberto Mondesi does not measure up as well. He hit a reasonable .276 last season in spite of striking out at a 26.5% clip. He never walked (3.8% BB%) and chased too many pitches outside of the strike zone (37.1%). Worst of all, he whiffed at 18.2% of the pitches he swung at, one of the worst marks among fantasy-relevant players. Owners are drafting Mondesi as a "safe" category stuffer, but his plate approach is so bad that his batting average and OBP could crater to unrosterable levels.

Aggression or passivity at the plate can confound the analysis slightly. For example, Mondesi was extremely aggressive last year with a Swing% of 54.9%. The league average was 46.6% in 2018. Even if a hitter has a high whiff rate, he can't strike out if he resolves the PA before three pitches are thrown. Votto is on the opposite side of the spectrum, as his refusal to swing at borderline pitches (39.7% Swing%) leads to more Ks than his SwStr% numbers would suggest.

Other plate discipline metrics exist, such as Z-Swing%, O-Contact% and Z-Contact%, but SwStr% is usually a good enough proxy for fantasy purposes. One exception to this rule is if an older player sees a decline in Z-Contact%, indicating that he can no longer make contact on pitches he used to hit in the zone. Another is a change in SwStr% rooted exclusively in pitches outside of the zone. Sometimes, missing those pitches is better than hitting them.

To conclude, both K% and BB% are useful for fantasy purposes but fail to tell the whole story. SwStr%, or how often a batter swings and misses, is a better indicator of a player's future strikeout rate than K% alone. O-Swing%, or how often a batter chases pitches outside of the zone, performs similarly concerning BB%.

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