From Bill James's website
These are the best hitters of all time at their positions and all of these men are in the Hall of Fame.
On the first list, six of the top nine leaders in career Runs Created by a catcher are in the Hall of Fame. The three who are not in the Hall—Piazza, Simmons, and Torre—have another thing in common. They do not have good defensive reputations at the position that is arguably the most important defensive position in the game, catcher.
If it was true that Piazza was not a good defensive catcher, I would be OK with him not getting into the Hall on the first ballot. I still think the best hitting catcher of all time should be in the Hall, but having to wait a few years wouldn’t be so bad. But, all the statistical measures suggest otherwise. In fact, they suggest that Piazza was an above-average defensive catcher.
The one thing that Piazza did not do well defensively was throw out basestealers. He allowed a 76.8 percent stolen base percentage in his career. Other catchers who caught the same pitchers as Piazza threw out 64.5 percent. However, nabbing basestealers is only a part of a catcher’s defensive responsibility and only a small part of Piazza’s overall game. It would be like saying that the best hitting second baseman of all time, Rogers Hornsby, shouldn’t be in the Hall because he didn’t steal a lot of bases in his time.
The most important part of a catcher’s job is handling his pitchers and in this area Piazza was superb. Here is one of the most telling statistics. In his career behind the plate, pitchers had a 3.80 ERA when Piazza was catching. If you look at all the other catchers who caught the same pitchers in the same year that Piazza did, they allowed a 4.34 ERA. That’s a major difference, much more important than a few extra bases stolen. (In fact, Piazza’s catcher ERA of 3.81 includes the run value of any extra stolen bases he allowed.)