catcher defense

The 2019 card set introduces a new defensive rating for catchers along with a new CFR range on the pitcher card. The purpose of these changes is to better model the defensive contributions by catchers.

Before we dig into the new system, let’s first examine the deficiency that it is intended to address. Previously, catcher defense was encapsulated by the arm, error, and wp/pb ratings. However, given that the error rating mostly matters on stolen base attempts (SB + E2?), and the pitcher ratings tend to be more determinative on wp/pb plays, a catcher’s defensive contribution was primarly a function of his arm rating.

We can use linear weights to estimate the run value of SB/CS. While the historical values vary based on run environment, we’ll keep things simple here and use +0.2 for a SB and -0.5 for a CS. So, let’s say we have a catcher with a great arm who threw out 50% of 70 attempts. That’s 35 SB * +0.2 = +7 runs, 35 CS * -0.5 = -17.5 runs, for 10.5 runs saved from SB/CS. In most recent MLB seasons the average success rate has been right around our assumed break-even rate (5/7, or approximately 71%), meaning we can treat an average catcher as effectively neutral. So, our catcher with the great arm was worth about 10.5 runs above average in MLB.

However, managers in the IBL generally do not steal when the projected success rate is under 65-70%. A typical cutoff for an attempted steal in a Manager’s Instruction Sheet is an adjusted stealing rating (ASR) of 8 or 9. This means our catcher who is saving 10.5 runs in MLB due to a 50% CS rate is unlikely to achieve this in the IBL, he simply won’t have enough opportunities to rack up the CS. The primary value of the great arm rating will be from the overall reduction of SB attempts. The success rate in the IBL tends to be around 75% (above our break-even point), so the reduced attempts do have positive value. Still, it’s unlikely this catcher will come anywhere close to saving 10 runs on defense in the IBL. Furthermore, given the relative difficulty of generating net positive runs from stealing (remember break-even is 71%), even the difference between a “good” catcher and a “bad” catcher is going to be limited.

Now, let’s compare our great defensive catcher with the potential difference between great defense and average defense at other positions (A vs F range, IFR/OFR plays):

      1b     2b     3b     ss     lf     cf     rf
runs  15-17  20-22  20-22  23-25  19-21  25-27  18-20

The best catcher is likely to provide less than 50% of the potential defensive value available at the least demanding position on the field (first base). The essential problem here is that while catcher is considered to be a critical defensive position, the way the game modeled catcher’s defense they actually deliver by far the least amount of defensive value. The “missing” catcher defense has effectively been transferred over to the pitcher. The purpose of adding a new defensive rating for catchers is to move enough defensive value back to the catcher so that their defense is appropriately scaled in relation to other positions. Hence the implementation of the catcher’s framing rating and the CFR play.