Glossary

A brief explanation of the metrics used.

bwoba

An estimate of the player’s “true” woba. This is estimated by looking at each plate appearance and modelling the outcome with a hierachical model. Roughly speaking, woba ~ (1|pitcher) + (1|batter) + platoon_advantage + (1|park).

wobacon

This is similar, but restricted to plate appearances where the batter makes contact.

whiff

The probability of a batter whiffing on a pitch. Again, modeled as whiff ~ (1|pitcher) + (1|batter) + platoon_advantage.

Three True Outcomes

This is the probability of a player’s plate appearance ending in a given outcome. This is modeled using a multinomial model with classes HR, BB, K, and other. The linear model is roughly outcome ~ (1|pitcher) + (1|batter) + platoon_advantage + (1|park).

Swing Decision Value

A batter’s run value added per pitch in the given attack region. Attack regions are defined in the same way as statcast. I model the probability of a batter swinging as swing ~ (attack_region|batter) + (attack_region|count). The run value of swinging on a pitch for a given attack_region and count is then calculated. From there I can compute the expected run value added for swing decisions in an attack region on a per batter basis. Note that this does not take into account a players ability to make contact. Swinging on a pitch in the chase region on a 2-1 count is generally a bad idea, but might make sense for batters with extreme contact skill. This will unduly punish such players.

Pitch cards

For each pitch in a pitchers arsenal, I show some release metrics. The data is all from statcast, and the derived quantities are based on Alan Nathan’s work.

Spin Vector

This is the spin axis of the ball at release as seen from the catcher’s POV. A filled dot at the tip means the vector is coming out of the screen, and a cross means that the vector is directed into the screen.

Release Consistency

The area of the uncertainty ellipse for the horizontal/vertical release angle. This is Max Bay’s idea.

Release Speed

Average release speed in mph as reported by statcast.

Total Spin Rate

The magnitude of the spin vector.

Acceleration

This is the acceleration in ft/s/s of the pitch that is not due to drag or gravity. It is a proxy for the amount of movement a pitch has due to spin and seam effects.