Arthur: The impact of the evolving strike zone

From SABR member Rob Arthur at on September 10, 2014:

The strike zone is a superficially simple concept kept constant in MLB’s rulebook, except for minor changes, for more than a hundred years. But in the past six seasons, the strike zone itself has evolved noticeably, and this change has impacted all aspects of the game.

MLB’s strike zone is defined as the space between a space over home plate, which is as high as the midpoint between the top of the shoulders and the top of the pants and as low as the bottom of the knees. Yet while the rulebook boundaries of the strike zone have stayed exactly the same since 1996, the advent of Pitchf/x has allowed us to measure the de facto limits of the zone, as actually called by umpires.

Since Pitchf/x data has become available, the strike zone has become more narrow but also taller. In particular, the area toward the bottom of the zone has expanded. The addition of this new territory has not gone unnoticed by pitchers. Instead, they have begun to aggressively exploit it with lower deliveries and more pitches with sinking action.

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Originally published: September 10, 2014. Last Updated: September 10, 2014.