It’s our 50th episode! We’re celebrating the start of the 2015 MLB season by answering reader questions, going through our draft results for our teams with an eye toward strategy for upgrading your team in season, talking about some of our favorite story lines for the year, and of course mentioning the best things we saw this week.
One of our reader questions is about converting defensive ratings to TAv (True Average) so that you can use the platoon splits for TAv and include defense.
The official Scoresheet rules packet says:
A difference of .10 in fielding range is a difference of .1 (a tenth) of a hit per nine innings that your pitchers will give up. We have come up with a fairly simple rule of thumb when comparing 2 players at the same position. For a full time player, each .10 in range is worth about .025 in batting average
Research by Scoresheet players has culminated in a commonly agreed upon rule of thumb that every 0.10 increase in range factor is worth about 0.055 in OPS. We assume that this 0.055 in OPS is comprised of an 0.025 increase in OBP and an 0.030 increase in SLG (which aligns with the rule of thumb from Scoresheet, more or less).
If we use the rule of thumb for calculating TAv, we can convert that this 0.055 of OPS is worth about 0.019 or 0.020 in TAv, or so:
TAv (estimated) = ( 103 * OBP + 43 * SLG ) / 200
So we get:
TAv (estimated change) = (103 * 0.025 + 43 * 0.030) / 200 = 0.019325
Of course, this is all based off of rules of thumb, casual estimators for complicated rate value metrics, and is meant as a way to make cursory calculations for quick eye balling of relative value. Hence, we suggest that you consider a range rating difference of 0.010 is equivalent to roughly 0.020 of TAv.