We all know the great catchers -- Johnny Bench, Pudge Rodriguez, Yadier Molina -- but only in the past few years have smart teams like the Yankees and Rays begun to pinpoint a main attribute that makes a catcher great: the ability to frame a pitch. Catcher framing is an act of subtlety, receiving the ball close to the chest, never stabbing at it, and turning pitches that nick the border of the zone -- or at least appear to -- into called strikes. Though framing is an almost indiscernible art form, it is now quantifiable. Baseball Prospectus has developed metrics that measure, in essence, the extent to which catchers are responsible for the calls that go their way. When you consider how many times a good framer influences at-bats, and how many runs that can save during the course of a season, you see how truly valuable he is to his team. Now that's a great catcher.