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Who’s going to catch Tim Wakefield‘s knuckleball? That’s one question Red Sox fans have been wondering since Doug Mirabelli was traded to San Diego. Mirabelli caught Wakefield almost exclusively–his “personal catcher.” Josh Bard appears to be in position to inherit Mirabelli’s role, continuing the tradition of a personal catcher for the knuckleballing Wakefield.

Though there are examples prior to the 1990’s–Tim McCarver catching Steve Carlton almost exclusively, for example–the phenomenon of the personal catcher has become more prevalent in the the past 15 years. Greg Maddux‘ preference of Eddie Perez (also Paul Bako or Henry Blanco in later seasons) over regular catcher Javy Lopez is well documented. John Flaherty was Randy Johnson‘s personal catcher in 2005. The unique demands of catching the knuckleball has meant that Mirabelli has worked with Tim Wakefield for the past several seasons, giving Jason Varitek the night off.

Giving the primary catcher periodic rest is one of supposed benefits of this arrangement. With the personal catcher playing every 5th day when his pitcher’s turn in the rotation came up, it created a pattern of 25-30 games per year the regular catcher would have off. This rest, in theory, would help the regular catcher from getting worn down over the course of a long season, remaining fresh enough even in September to contribute offensively. It is this question that interests me today–do personal catchers provide a measurable boost to their primary counterparts by allowing them periodic rest? Does the fact that Tim Wakefield has Josh Bard (and previously, Doug Mirabelli) as a personal catcher help Jason Varitek stay productive in September?

We can use the BP database to help answer the question. First, we need to determine who has been a personal catcher. While it’s possible to research individual seasons and statements by managers about assigning a certain catcher to a pitcher, we can also look at the actual usage patterns to identify these situations, as well as any “de facto” personal catcher arrangements that may not have been made explicit. For our study, we’ll define a personal catcher as one who caught one pitcher at least 20 times, while starting no more than 50 games total. This captures the fact that (a) a personal catcher works primarily with one pitcher, and (b) the personal catcher is not a fulltime player, nor even in a balanced jobshare or platoon.

By this standard, I identified 42 instances of personal catchers since 1960:

YEAR TEA CNAME                PNAME                  GS TOT_C_GS TOT_P_GS
---- --- -------------------- -------------------- ---- -------- --------
2005 BOS Doug Mirabelli       Tim Wakefield          29       33       33
2005 CHN Henry Blanco         Mark Prior             23       48       27
2005 NYA John Flaherty        Randy Johnson          21       39       34
2005 PHI Todd Pratt           Jon Lieber             21       49       35
2004 BOS Doug Mirabelli       Tim Wakefield          30       41       30
2004 CHN Paul Bako            Greg Maddux            32       43       33
2004 HOU Raul Chavez          Roy Oswalt             33       48       35
2004 SDN Miguel Ojeda         Ismael Valdez          20       37       20
2003 ATL Henry Blanco         Greg Maddux            33       42       36
2003 BOS Doug Mirabelli       Tim Wakefield          32       43       33
2003 HOU Gregg Zaun           Jeriome Robertson      24       26       31
2003 TEX Todd Greene          John Thomson           20       49       35
2002 ARI Rod Barajas          Miguel Batista         27       41       29
2002 SFN Yorvit Torrealba     Ryan Jensen            22       40       30
2001 ATL Paul Bako            Greg Maddux            34       45       34
2001 HOU Tony Eusebio         Shane Reynolds         24       40       28
1999 TBA Mike Difelice        Wilson Alvarez         20       50       28
1998 ATL Eddie Perez          Greg Maddux            32       39       34
1998 HOU Tony Eusebio         Shane Reynolds         29       45       35
1997 HOU Tony Eusebio         Darryl Kile            27       42       34
1996 MON Lenny Webster        Jeff Fassero           30       50       34
1996 NYA Jim Leyritz          Andy Pettitte          27       50       34
1994 ATL Charlie O'Brien      John Smoltz            21       42       21
1994 HOU Tony Eusebio         Greg Swindell          20       41       24
1992 CAL Ron Tingley          Bert Blyleven          22       46       24
1992 MIN Lenny Webster        Scott Erickson         24       32       32
1991 CHA Ron Karkovice        Charlie Hough          20       49       29
1991 MIN Junior Ortiz         Scott Erickson         28       41       32
1991 MON Ron Hassey           Dennis Martinez        21       34       31
1988 MIN Brian Harper         Allan Anderson         24       41       30
1987 TEX Geno Petralli        Charlie Hough          21       49       40
1983 CIN Alex Trevino         Mario Soto             33       50       34
1979 BAL Dave Skaggs          Dennis Martinez        35       46       39
1979 PHI Tim McCarver         Steve Carlton          27       31       35
1978 PHI Tim McCarver         Steve Carlton          34       34       34
1977 PHI Tim McCarver         Steve Carlton          36       39       36
1976 PHI Tim McCarver         Steve Carlton          31       37       35
1974 ATL Paul Casanova        Carl Morton            21       29       38
1972 MIN Phil Roof            Bert Blyleven          20       48       38
1970 ATL Bob Didier           Phil Niekro            20       48       32
1970 BOS Tom Satriano         Sonny Siebert          26       47       33
1966 CLE Del Crandall         Sam McDowell           24       39       28

For each of these personal catchers, I took the catcher on the team with the most games started and made that the group of “primary catchers” (the personal catcher thus being “secondary” catchers). I then took every catcher who started 100 or more games in a season and was not on a team with a personal catcher as the group “fulltime catchers.” The goal was to determine whether primary catchers (who benefit from periodic games off) fared better late in the season than did fulltime catchers.

I took the aggregate performance of all primary catchers through the end of August, and compared it to the aggregate performance of the group in September/October (regular season games only). I then repeated the process for fulltime catchers.

                   Through August     After Sept. 1st    Difference
Category           AVG/ OBP/ SLG      AVG/ OBP/ SLG      AVG   / OBP  / SLG
Primary Catchers  .267/.329/.376     .257/.321/.351     .01019/.00797/.02546
Fulltime Catchers .265/.332/.410     .263/.329/.396     .00225/.00246/.01383

As might be expected, both groups lost some amount of productivity in September, resulting from a combination of the fatigue of a long season and the cooler weather arriving, which depresses run scoring slightly. And one group did indeed lose significantly more production than the other. Surprisingly, it was the primary catchers, who have the benefit of regular rest from the secondary personal catcher, who lost more offense. Fulltime catchers only dropped about 2 points of AVG and OBP, and 14 points of SLG, while primary catchers lost 10 points of AVG, 8 points of OBP, and a whopping 25 points of SLG. Overall, fulltime catchers lost about 16 points of OPS in September, while primary catchers lost double that amount (33 points).

So does the data above prove that personal catchers are actually a hinderance to the primary catcher? Does getting every 5th game off during the year actually cause a September slump? Not really. Note, for instance, that fulltime catchers as a group outhit primary catchers both time periods, particularly in the power category of SLG. It may be that stronger catchers hit for more power, and stronger catchers hold up better over a long season. Personal catchers didn’t cause the decline in late-season offense for their primary catchers; it is mere coincidence that primary catchers as a whole weren’t as good at hitting to begin with. Perhaps managers are more inclined to grant a veteran pitcher a personal catcher (and most of the pitchers on the list were veterans) when the primary catcher is known to be fragile, aging, or prone to tiring late in the season to begin with. The rest enabled by a personal catcher could be forestalling an even greater decline than has been observed. Perhaps periodic rest is not what’s important, but rest when the catcher is actually feeling fatigued. Thus, a manager who gives the backup 30 starts based on the regular catcher’s status regardless of who might be pitching that day is more beneficial than a personal catcher arrangement. Any of these are plausible reasons for what we observed. However, what we can say is that there isn’t an immediately obvious benefit to a team’s regular catcher by having his off days come on a regular basis due to a pitcher having a personal catcher on staff.

Of course, resting the other catcher isn’t usually the main reason a personal catcher arrangement is instituted. It’s typically driven by the pitcher’s request, based on who he’s more comfortable working with, or by a pitcher’s unique requirements such as Wakefield’s knuckleball. But the expected side benefit of scheduled rest for the regular catcher doesn’t appear to have significant value over ad hoc decisions to give him the day off. So even if Tim Wakefield doesn’t end up throwing exclusively to Josh Bard, there’s no reason to think that the changed situation will affect Jason Varitek’s bat down the stretch.

Thank you for reading

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