How Well Did "Replacement" Catchers Actually Hit?

I looked at the top 100 or so catchers in career PAs since 1945. Then I looked for catchers who had a season with a 200+ PA decline followed by a season with a 200+ PA increase. So they went down at least 200 PAs from season 1 to season 2, but then from season 2 to season 3 they went back up at least 200 PAs. They had to be on the same team all three seasons. I then calculated the OPS+ of the "replacement." All data was from Baseball Reference.

The idea is that these catchers were temporarily replaced. Catcher is a position for which it is probably very hard to simply move a guy from another position. In the outfield, you can move a right fielder to center, for example. Maybe move a SS to 2B or a 3B man to 1B. But at catcher, you really need to find another guy who is a catcher.

Unfortunately, there were not many cases. Only 11. And I used two seasons for Fisk, 1974 and 1975. He came back to being a regular in 1977. In almost all cases, the catcher had 400+ PAs in both season 1 and season 3.

Then I found the difference in PAs for each player, comparing season 1 to season 2, and season 2 to season 3. A catcher might have 500 PAs in season 1, then 200 in season 2 and 450 in season 3. So in one case I could assign 300 PAs to the "replacement" catcher and 250 in the other.

That means I did two calculations for the OPS+ of the "replacement," one using the difference in PAs between season 1 and season 2 and the other using the difference in PAs between season 2 and season 3. The "replacement" OPS+ is a weighted average of the OPS+ of the X number of PAs for catchers on the team in season 2 who ranked lowest in OPS+.

For example, if a team needed to replace 300 PAs at catcher, I ranked any catchers on the team from highest to lowest in OPS+. Then I came up with a total number of PAs that equaled 300 using the lowest ranked catchers in OPS+ on the team. It might be 100 PAs from one catcher and then 200 from another. Then I calculated their combined OPS+, weighted by PAs.

The table below shows the OPS+ for the replacements. ROPS+1 refers to the OPS+ of the "replacement" assuming the number of PAs needing to be replaced is the difference in the regular starting catcher's PAs from season 1 to season 2. ROPS+2 is for the season 2-3 difference. The last column shows the OPS+ for the regular starter over the three seasons in question.

Player	Year	ROPS+1	ROPS+2	St. OPS+
Alomar	1999	61	58	76
Crandall	1961	91	82	110
Fisk	1974	61	61	122
Fisk	1975	52	52	122
Girardi	1991	68	59	71
Kendall	1999	26	27	129
Lieberthal	2001	63	63	105
Lopez	1999	67	67	117
Posada	2008	48	46	135
Scioscia	1983	66	66	92
Varitek	2001	78	78	93

Generally, the replacements did much worse. ROPS+1 has a weighted average of 64 while ROPS+2 has a weighted average of 60. The weighted average of the OPS+ for all these catchers, over the three seasons (4 for Fisk) is 109. All catchers with 1000+ career PAs since 1945 had a combined OPS+ of 92 (also a weighted average).

So when teams have had to "replace" their regular starting catcher, temporarily, the "replacements" had an OPS+ in the range of 60-64 while an average catcher would have had 92. But the drop off compared to the actual starters on these specific teams was even greater, since they a had a combined OPS+ of 109.

Why the guys who needed to be replaced tended to be above average is not clear. I did look at the guys with the longest careers and maybe one of the reasons why they had long careers is that they generally hit better than average catchers.

Again, I only had 11 observations. So the conclusions from this might be limited. Maybe this analysis will give other people some ideas on how to approach this issue.