Sarris: Five thoughts on Statcast’s new infield defense statistic

From SABR member Eno Sarris at The Athletic on January 13, 2020:

Infield defense has long been one of the most difficult aspects of baseball to assess, especially statistically. Just think about how many skills are involved with every play: There’s the defender’s positioning before the ball is hit, the reaction time as he figures out where the ball is going, the first step toward that direction, the speed at which he can get there, the technique involved in staying in front of the ball, the softness of the hands as they pick it, the steadiness (and quickness) of those hands as they ascend, the transition into the throwing hand, the strength of the throw, the accuracy of the throw, and then the skill of the first baseman at receiving the throw.

That’s a complicated set of individual moments that add up to a single defensive play, and many of those — like positioning — aren’t even necessarily totally in the control of the defender. And before the days of deep data, before player tracking was a part of baseball’s reality, there weren’t any numbers to describe most of those things. Most defensive stats relied on creating defensive zones and judging which players did the best at turning balls in those zones into outs.

But now Statcast exists, and we know how hard the ball is hit, and where the player started, and how fast he was at getting to the ball, how fast the runner is — we know how far the player had to go to get the ball and how much time he had to make the play. We can judge how hard the play was and know which players made the harder plays.

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Originally published: January 13, 2020. Last Updated: January 13, 2020.