Angels pitching has been extremely frustrating to watch (well, not so frustrating last night) because of a frequent inability to throw strikes. I wondered, is there any evidence that the catching can make a difference? A catcher can cost a pitcher a strike if he moves too much while catching a pitch, or blocking the ump from seeing a portion of the zone ("get down, Napoli!"). Some say a catcher can buy a strike by framing a pitch, but if they are too obvious about it the umpire may be inclined to call a ball. I looked at retrosheet's data to see what difference, if any, I can find in pitcher walk rate between Jeff Mathis and Mike Napoli.
What I did was look at all pitchers from 2005-2009 who faced at least 50 batters with Napoli and Mathis behind the plate. Then I pro-rated the Napoli walk rate to the Mathis plate appearances. The difference is big enough to notice. Our pitchers overall walked 9 percent more batters when Napoli was catching. Over a full season of 6200 plate appearances, this works out to 37 more walks, or about 12 runs. And higher pitch counts. Weaver was typical (8%), the differences for Saunders (37%) and Santana (39%) were more extreme.
I don't know if this is a fluke, or a repeatable skill. Most studies of catcher skill like this have not been shown to have any predictable effect for the future. I don't have any conclusions to offer, and don't know if it means Napoli is terrible, or that Mathis is a catching god, or something in between. What we've seen is a stretch of games where Napoli has caught virtually every game and our pitchers have walked way too many. I wonder if Mike Scioscia is thinking "I told you so" to us fans who criticized making Mathis the starting catcher at the beginning of the season. In Sosh we must trust.