Aramis Ramirez looks to be out another day today with his sore shoulder. We know that he’ll need surgery on the shoulder at the end of the season, and it’s a little bit of a concern that it seems to be getting more painful for him as the season goes on. With the Cubs two games in back of the Cardinals, they need every at-bat they can get from Ramirez, who’s been the team’s best player this season - Fangraphs puts him at about a win and a half better than replacement over the just 182 plate appearances he’s had so far this year.

But what if Ramirez needs to miss extended time, or is done for the season? At this point the most likely answer is that Jake Fox would take over at third base. Nobody questions that Fox is a decent hitter. He’s hit very solidly in the majors, and in AAA this season he absolutely destroyed the ball. He’s probably not as good as he’s been so far this year, but his ZiPs projection from Fangraphs is for a .329 weighted on-base average the rest of the season. That’s very close to average in the majors.

Fox’s defense, though, is a problem. Fox is roughly as much of a third baseman as I am, according to the scouts, and I haven’t played baseball since high school. He’s actually put up 135 innings at third this season, though, and been slightly above average in those innings, .5 runs above average (or over the course of a whole season, about four runs above average). But we can’t really expect that to continue - it’s more likely the scouts were right and Fox isn’t very good at third, a position he had to learn when he couldn’t stick at catcher and at which he’s still a work in progress, to be generous.

I don’t really know how bad Fox’s defense would be if he played third every day, but let’s just assume the worst for now. Among qualified players at 3rd base, Chipper Jones has the worst UZR/150 this season, at -20.7. Basically, for every 7.5 games Jones plays at third, he costs his team a run with his fielding. That’s about two wins a season. Let’s assume, for the sake of argument, that that’s how bad Fox’s fielding would be if he played every day.

The Cubs have 53 games left. Using the hypothetical “as bad as Chipper in the field” numbers, that would mean Fox was worth about -7 runs with his glove over the rest of the season, compared to average. Assuming his .329 ZiPs projection is about right, he’ll be roughly average with his bat, so we’ll say that he’d be worth about seven runs less than an average third baseman. (If you choose to assume Fox will keep hitting about as well as he has this season, and figure that he’d get around 200 more PA if he played every day, he’d be worth roughly nine runs above average with his bat, so figure two runs above an average third baseman.)

But Aramis isn’t an average third baseman. He’s very slightly below average defensively for his career, being 1.1 runs worse than average over 150 games. That’s basically negligible over 50 games. His ZiPS rest-of-season projection is a .382 wOBA, which would be about nine runs above average over 200 plate appearances. So at nine runs over average for the rest of the season, Aramis would be about 16 runs better than Jake Fox over the rest of the season, or about a win and a half, assuming Fox’s defense is as bad as advertised.

It might not be quite that bad. Fox’s minor league numbers in past seasons factor heavily into that projection, and the rumor is that he’s fixed a lot of holes in his offensive game. If that’s true he may be a better than average hitter in the long run, and can make up for some of the potential deficiencies with his glove. He may also be a few runs better with his glove than I assumed - 20 runs below average is very, very bad, and even a terrible third baseman could be considerably better than that. So the dropoff between Fox and Ramirez may not be quite as bad as all that - but I hope it doesn’t end up mattering, because if it really is a win and a half, this team can’t afford that at this point.