Now that Alex Gonzalez has gone on the disabled list, it appears that the position of shortstop is realistically up for debate. In Dusty Baker's eyes, Gonzalez was the starter and it was going to stay that way, but now that the starter is gone, who should replace him?
The two leading candidates are Jerry Hairston Jr. and Paul Janish (who?). Each player has his advantages, Hairston is a better hitter, Janish a better fielder. Some of the decision really depends on what you think the bigger need is for the Reds. To break it down a bit more numerically, let's take a look at how they project for the remainder of the season, using ZiPS from FanGraphs:
As you can see, Hairston projects to be a much better hitter over the remainder of the season compared to Janish. The difference between the two over 250 plate appearances is about 8.5 runs, or pretty close to a win. That's quite a dramatic difference over that few plate appearances. Even if Hairston's projection is a little high, as it appears to be to me, he has a lot of room to fall. His bat is clearly superior to Janish's.
Defensively, it's a bit harder to pin down. While I doubt anybody would argue that Janish is not the better defender, to what degree this is true isn't easy to make clear. So far this year, according to UZR, Hairston has actually been a better shortstop than Janish by about a half of a run, though both are in minutely small samples. Chone Smith projects Janish at as a +1 defender over 150 games, while Hairston projects to about -5 at shortstop. If we prorate that to one-third of a season, we're only looking at approximately a 2-run difference defensively. Given that, I'd have a hard time putting Janish at shortstop instead of Hairston.
Then again, there is the matter of third base. Until Edwin Encarnacion comes back, the Reds need somebody to play third base, and the choices right now are basically Hairston or Adam Rosales. Rosales projects to be a slightly better hitter than Janish, but defensively he is projected to -7 runs over 150 games at 3B. He's done much better than that this year (+1.4 runs), but I'm not convinced that his number this year are anything but small sample sized luck. And given that I'm less confident in his offensive projections than I am Hairston's, I think I'd rather see Hairston at 3B and Janish at SS until Encarnacion comes back.
After Edwin comes back, I wouldn't mind seeing Janish still getting some starts at shortstop mainly because I think having an excellent defender next to Encarnacion will help cover up some of his shortcomings. When Janish isn't starting, he should definitely be used regularly as a defensive replacement when the Reds have a lead. I know it's a lot to ask of Dusty to remember that Janish is on the team, but having a valuable defensive weapon at an important defensive position can be a real asset. Hell, Juan Castro built a whole career doing that, and he wasn't nearly as good defensively as Janish appears to be.