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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 Adam Dunn, Mark Reynolds, and 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 2015, the league average K rate was 20.4%, meaning that roughly one in five MLB PAs ends 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.
Sabermetrics may be used to determine whether a given player "deserved" his K rate 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 is around 10%, 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 popup a fastball over their head early in the count. In 2015, the league averaged an O-Swing% of 31.3%. Numbers significantly higher than this indicate an increased likelihood of chasing a bad pitch and 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!
Lets look at some examples of advanced plate discipline stats in action. Joey Votto is widely regarded as a master of plate discipline, and his surface stats support the assessment. His 20.6% BB% actually exceeded his 19.9% K rate, after all. Digging deeper, we find that these numbers are completely justifiable. His 19.3% O-Swing% was almost half of the league average rate, and his 7.7% SwStr% was above average as well. It is safe to conclude that Votto will continue to demonstrate outstanding plate discipline in 2016.
Baltimore's Adam Jones, however, may not be so lucky. A poor BABIP doomed him to his worst numbers since becoming an Oriole, but lost in the misery is a strong 17.5% K rate, a significant improvement over both his 19.5% rate in 2014 and his career mark of 19.5%. He even nearly doubled his walk rate from the previous year, though his 4.1% figure was still below the league average of 7.7%.
At first glance, this would set Jones up for a career year if his BABIP returned to normal. Advanced plate discipline stats disagree, however. His 47.7% O-Swing% was the highest of his MLB career and the second highest mark in all of MLB, besting only Boston's Pablo Sandoval. Likewise, his SwStr% remains higher than league average at 13.3%. Any 2016 Jones rebound will have nothing to do with the improved plate discipline suggested by his surface level rate stats in 2015.
Aggression or passivity at the plate can confound the analysis slightly. For example, Jones regularly outperforms his swinging strike rate by avoiding two strike counts. Even if a hitter has a high whiff rate, if he ends the at bat early, he can't strike out. The flip side of the coin relates to players who take too many early count strikes. A player can make a ton of contact. If he's frequently two strikes in the hole, he'll still pile up strikeouts.
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 rate alone. O-Swing%, or how often a batter chases pitches outside of the zone, performs similarly concerning BB rate. 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. The 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. That is usually a bad sign.
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