Catcher framing is the art of a catcher receiving a pitch in a way that makes it more likely for an umpire to call it a strike -- whether that's turning a borderline ball into a strike, or not losing a strike to a ball due to poor framing. The effects of a single pitch can be huge; in 2019, hitters had an .858 OPS after a 1-0 count, but just a .631 OPS after an 0-1 count.
Statcast's catcher framing numbers are primarily based on the edges of the plate (or the "Shadow Zone" in this image), the area that is the width of two baseballs (one inside the zone, one outside) all around the edges of the strike zone. Statcast's catcher framing is adjusted both for park and the pitcher. Read more about catcher framing here.
The numbers on the leaderboard are expressed in several different ways:
• Strike rate: Percentage of non-swings on the edges of the zone converted into called strikes. In 2019, Austin Hedges led with 54.1%, and Isiah Kiner-Falefa was at the bottom with 42.3%. The MLB average was 48.1%.
• Runs from Extra Strikes: Converts strikes to runs saved on a .125 run/strike basis. In 2019, Hedges had +20 at the top, and James McCann had -16 at the bottom.
• Zone breakdowns: Allow the strike rate to be expressed in eight different areas around the strike zone, as shown here.
In A Call
"In 2019, Austin Hedges converted 54 percent of takes into strikes on the edges of the zone, the best rate of any catcher in baseball."