In a few days, the Cubs will open regular season play with Luis Valbuena at 3B. Compared to the other options the Cubs have, he isn't that bad. Compared to other 3B, it's really bad.
The first thing I looked at when analyzing Valbuena's last season was to look at his BABIP. It was low last year, at .260. That gives you the impression he's bound to get luckier next season and regress to the mean…right? Unfortunately, that's not how it really works. Valbuena's career BABIP is .269. He's likely unlucky, but over 1109 PA you can start to be reasonably confident that he's never going to have an outstanding BABIP. He likely just makes poor contact; his true talent level is probably .280 to .290.
Even if he did have a BABIP of .300 last year, his line would translate (assuming his extra hits are seeing-eye singles) from .219/.310/.340 to .251/.338/.371. That's certainly a much better line, but still a poor one for a third baseman. .371 would be good for 34th among players with 200 more PA and 50 games at 3B, right behind Brandon Inge. We'd have to give him 3 more doubles (so 1/3 of his "found" hits) just to tie him with Brandon. His ISO is 32nd as well. He just doesn't have the bat to hack it at the corner.
It's not all bad for Luis. He can play 2b reasonably, and he can even play shortstop in a pinch. His bat is much more suited to play at 2B, where he doesn't need to hit the cover off the ball to be productive. Unfortunately, that's not where he's needed on the Cubs. Instead, he's a punchless threat that needs hit-luck just to be bad offensively (and that luck isn't all that likely to come: a .280 BABIP provides a translational .235/.324/.355) from a position that almost demands more power than that. Cubs fans have to hope that Lake takes a serious step forward and takes the position from Valbuena in the second half of 2013, because Luis is just not the answer at the hot corner.
A side note on positional value adjustments:
I try to break the positions into 2 equal groups: offensive and defensive positions. The 4 positions up the middle of the infield (C, 2B, SS, CF) are way harder to field adequately. You can be bad at the plate and good on the field and still be average. In contrast, the outer positions (1B, 3B, LF, RF) are much easier to field, so the offensive burden is much greater. Even if you are league-average offensively, you're a below-average player if you field any of these positions (unless you are absolutely stellar in the field – even then, the amount of defensive value you can provide is limited). This is why Darwin Barney at 2B can be an adequate player with a .300 OBP while Valbuena at 3B would be a poor one even at a .338 OBP (Barney also plays sublime defense at 2B while Valbuena is merely good at 3B, and likely average to below-average at 2B).
This is also a useful tool in explaining why it's so good to have a player like Starlin Castro. The theoretically average team would have 4 good hitters and 4 bad ones, given how positions are. Castro is a good offensive player from the defensive spectrum, which is historically uncommon (CF are really good right now, historically. SS were up 10 years ago. This things ebb and flow). That allows us to add a threat that the average team won't have (or masks a weakness we might have from a traditional "power position"). DeJesus can also add that to our team if he can make it defensively in center (I don't think he can, but he'll get every chance to). Unfortunately, the Cubs squander that by taking a bath at 3B and RF, so we end up at even anyways…