Repertoire and Results: The Leading Indicator for Good Pitching

Last week, I wrote about the most- and least-effective pitch combos and the pitchers who were using them well. This started us down the road of answering the question “who is using their pitch repertoire the best”?

Anecdotally, we saw a correlation between ‘effective repertoire usage’ and ‘good pitchers’. I wanted to quantify that relationship better to see if there really was a statistical relationship between pitchers who use their repertoire effectively and objectively ‘good’ pitchers.

To do this, I calculated the actual wOBA allowed for each pitcher and the Combo Repertoire wOBA Addedfrom the 2018 seasons. My hypothesis was that there should be a positive correlation between these two measures of effectiveness because the Combo Repertoire wOBA Addedwould be an input or leading indicator of overall wOBA Allowed.

The chart showing these results is below. To try and eliminate as much noise as possible from low-innings pitchers, I filtered to only pitchers with combo sample sizes >= 300. The size of the dots also represents sample size (larger = higher n). The X-axis is Combo Repertoire wOBA Added and the Y-axis is 2018 wOBA Allowed. Dot color is also shaded to show wOBA Allowed.

The resulting r-squaredbetween Combo Repertoire wOBA Added and 2018 wOBA Allowed is ~0.2; which is good enough to say this is a relationship between the two measures.

Practical Implication

Effective pitchers use their pitch combo repertoire effectively. Pitchers who are good at getting hitters out do so because they use the 1-2 pitch combos that give them the most success more often; and they avoid the combos that hitters hit well. Less effective pitchers either lack any effective pitch combo to go to, or they are underuse them.