The Value of the Count
To determine the best pitch to throw in a given situation, we must first know the value each pitch adds to a team. To know the value each pitch adds, we must know the relative starting and ending points positions of the pitcher vs. batter relationship. There are many factors that contribute to this, but the most important one and the factor we will explore in this post is the balls & strikes count.
We chose Weighted On-Base Average (wOBA) as our key metric to measure since this is a widely-recognized metric as being highly indicative of a hitter’s value and can be converted to Weighted Runs Above Average (wRAA), an easier-to-understand metric and more relatable to wins and losses. Another key decision we made was we didn’t use ‘historical’ wOBA (as determined by the actual outcome of at-bats) but rather, MLBAM’s expected wOBA using launch-speed and angle. Our goal was to remove noise and variation from defenses, and instead, just focus on the quality of contact by the hitter. This is due to our hypothesis that hitters can affect quality-of-contact, and thus, should be rewarded for weak ground balls induced. They shouldn’t be punished for an errant throw by the third-baseman.
To understand the relative position of pitcher vs. batter through the course of an at-bat, we looked at each pitch thrown, the resulting count, and how that at-bat ultimately ended. That is, we didn’t pay attention to the outcome of the pitch on that count, but rather, how the at-bat ultimately ended – which might have been several pitches later. Thus, this equates to a hitter’s chance of eventually getting on-base if they reach the given count.
The table below shows the fairly intuitive result: each marginal ball increases the expected wOBA, and each strike decreases it. If a hitter hits a 3-ball & 0-strike count, then they have a 0.561 wOBA. An 0-2 count has a bleak 0.180 wOBA.
Sorting this same table by wRAA shows us the run-value of reach each count. Hitting 0-2 detracts 0.10 wRAA from the hitting team, and reaching 3-0 adds 0.22 wRAA for them.
Now that we know the relative value of moving from any count to the next (e.g. going 2-1 to 2-2), we can assign a value to the pitch that moved the pitch and hitter there.