June 18, 2024

As spring training begins in Florida and Arizona, sports pages are full of the typical clichés. Seemingly every player is reporting to camp in the “best shape of their life.” Teams are excited to take it “one day at a time.” Almost every pitcher tells an eager reporter that their arm is “feeling great.” What has also become a common point of discussions in the stories that feature these simple clichés is hitters talking about adjusting their approach for the coming year.
“The St. Louis Post-Dispatch” recently reported that Cardinal’s slugger Matt Holliday has spent the off-season pleading with teammate Matt Carpenter to be more aggressive at the plate. Carpenter, the two-time all-star, is known throughout the league for his patient approach. Similar news out of Cardinal’s spring training includes Jason Heyward attributing his decline in power hitting to the more patient approach he opted to take, which happened after his former team, the Atlanta Braves, moved him to lead-off spot in the line-up. While the talk of changing hitting approaches is not exclusive to the Cardinal’s camp (similar stories have emerged from the Mets, Brewers and Red Sox camps, just to name a few) stories always give credence to the vague conjecture offered players. However, baseball, where every action is recorded and clearly defined goal exists, is the one area of life that has the potential to be devoid of vague conjecture. While Holliday and his colleagues suggest that a more aggressive approach in the batter’s box will lead to more optimal results, the question should not be approached through the mere anecdotal evidence from players.
The assumption that underlies, what we will call the Holliday hypothesis, is that swinging at more pitches will lead to more power. Testing this theory is relatively easy. Fangraphs — a leading baseball think tank — keeps records on the swing percentage (meaning the percentage of pitches swung at) and isolated slugging percentage (which is slugging percentage minus batting average and is generally accepted as the best metric of pure power). If the Holliday hypothesis were to ring true, there would obviously be a strong correlation between the two numbers. Examination of team-level data for the 2014 season does give some credence to the Holliday hypothesis. A regression analysis between the two values demonstrates that 18 percent of the variation between teams’ isolated slugging percentage in 2014 was attributable to the difference in a team’s swing rate. It should also be noted that the Holliday hypothesis is muddled in causation problem. Teams that are more successful have more incentive to swing, raising the question: do teams that swing more have more success, or do teams with more success swing more?
However, what the Holliday hypothesis does not account for is the cost of swinging. Free swingers are notorious for low-walk rates and on-base percentages. When a batter swings at the ball, the best possible outcome is the hitter makes contact and puts the ball in play. In Major League Baseball, 70 percent of the time a batter puts the ball in play he records an out, according to FanGraphs.
However, when a batter takes a pitch the best possible outcome is a ball. In the history of baseball a ball has never lead to the batter being out. As noted earlier, swing percentage explains 18 percent of the variance in isolated slugging, but also changes in swing percentage explains 50 percent in the walk rate (again using 2014 team level data).
What remains to be answered is whether the exchange worth it, as the Holliday Hypothesis suggests. The components of isolated power are certainly worth more than walks. Last year in the MLB, a double had a run value 1.9 times greater than that of a walk, while the value of a homerun was 3.1 times greater. However, ISO does not reflect this;  instead, ISO uses the outdated slugging percent valuation which holds that a homerun is four times more valuable than a walk. Given that swing-rate leads to less than variation in a metric that already overvalues power compared to walk rate — the Holliday Hypothesis is standing on shaky ground.

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