If you don't know who this is, he's the starting catcher for the Tampa Bay Devil Rays. Don't bother getting familiar with him. He's horrible.
He's hitting .179/.241/.250, for a robust .491 OPS. He's a starting catcher who at the plate is far below replacement level for a catcher. According to BP, he's 12 runs below replacement. Makes you wonder if he's that far below replacement, why don't they replace him? Surely someone in the Tampa Bay minors could manage a .491 OPS.
How does he keep his job? Well, according to BP he's pretty good defensively, at 12 runs above replacement. That gives him a WARP1 of -.1, or essentially replacement level when both hitting and defense are accounted for. But as discussed in the past, it is more widely accepted that fielding should be measured against the positional average, not against replacement. There, Dioner earns a 0. He's average defensively. If you recalculate his WARP1 based on FRAA, instead of FRAR, you get a -1.3 WARP through a bit more than half a season. (Look out Jerry Narron!)
Who can the Devil Rays promote? Let's start at the big club. Raul Casanova, Navarro's backup, has an OPS of .758. His slugging percentage is higher than Navarro's OPS. His defense is a little less robust, but that is made up for by his hitting.
Josh Paul, also with the big club, is not the answer with a .547 OPS. He's been DL'd twice this season, and most recently was put on the 60-day DL on June 3 (and he has not returned).
There are three players at AAA Durham: Hernandez, Johnson and Riggans. Hernandez is the best hitter, turning in an .820 OPS. You have to discount that for league quality. If AAA is 93% of MLB quality, that's still a .763. Johnson, the youngest, would be below replacement level at the plate, b/c he is struggling at AAA. Riggans has had a shot in the bigs (10 ABs, in which he did nothing and then went on the DL), and is only managing a .770 OPS at all levels. He probably isn't the answer.
Down at AA (Montgomery): they've got Jaso, Arhart and Spring (a good name for a catcher). The latter two aren't hitting and Arhart is on the 7-day DL, but Jaso has an .876 OPS, translatable to something like a .770 at MLB. He's outhitting SS prospect Reid Brignac and his OPS is second on the team to consensus Top 10 prospect Evan Longoria. He is slumping since the All-Star break, but I bet we see him in September.
That's at least three real possibilities: Casanova, a major league veteran; Hernandez, the Crash Davis of the system (but really only 28); and Jaso, the 23-year old future.
