No question: Jason Castro was signed to be the Twins primary catcher. But how primary?
Castro has averaged 105 starts behind the plate the past three years with Houston. Paul Molitor has reportedly told him he (Molitor) wants to start him 120-125 times this year.
I intuitively think that's too much. I'd rather see the left-handed hitting Castro deployed as part of a platoon -- Castro starting against right-handed starters, the backup against lefties. Certainly the pieces are there to do that, with backup contenders Mitch Garver, Chris Gimenez and John Ryan Murphy all right-handed.
Castro certainly has hit righties better than lefties. In 2016, for example, his OPS against righties was .757; against southpaws, .478. He's a .190 career hitter against lefties (505 official at-bats). Of course, the Twins didn't commit $24.5 million to him for his bat, and there's no platoon differential in the field.
Houston does not appear to have ever tried a straight platoon with Castro. Last season Castro started 81 of Houston's 109 games against righties and 21 of their 53 games against lefties. That leans toward a platoon, but is pretty loose.
Last year the Twins faced 46 left-handed starters and 116 right-handers. If repeated in 2017, that sort of splits the difference between 105 and 125. It may well be that even if Molitor were to adopt a strict platoon at catcher (at least in terms of who starts) that Castro would get more work than he did in Houston. And it would focus his at-bats against pitchers he has a chance against.