First off, I would like to state clearly and unambiguously that I am not about to take this position to be the Devil's Advocate. I am taking this position because I believe it to be an accurate depiction of the situation.
Kyle Lohse got screwed.
There are a number of parties who are to blame for this unfortunate circumstance, and I'll name names later, but let's first look at the things which Kyle has almost complete control over--strikeouts, unintentional walks (UIBB), and home runs.
Rather than expressing these rates per nine innings, I am going to express them per total batters faced (TBF). This is in general better practice, for reasons that will become clear later in the show. So let's look at what he did last year, this year, what his career numbers are, and what PECOTA expected from him before the season started.
SO/TBF UIBB/TBF HR/TBF
2005 0.112 0.051 0.029
2006 0.124 0.093 0.031
Career 0.139 0.069 0.032
PECOTA 0.120 0.059 0.032
Looking at these numbers, what do we see? Compared with last year, Lohse has actually improved his strikeout rate and his home run rate is practically identical. His walks are up. (Hence the bold highlighting.)
Actually, his walks are up quite a bit by looking at the rate. Is this a significantly large jump? I'd say no. The difference between Lohse pitching at a .093 rate and his career .069 rate is 4 walks. Any time 4 events makes the difference between a current number and a career number, I'm inclined to believe the career number more.
But in any case, Lohse's walks are up from last year, but his strikeouts are also slightly up from last year. It's not a total wash, though, as we can see from his Fielding IndePendent ERA.
So yes, Lohse still looks bad here, but his career FIP is right around 4.94, so it's not the disastrous start that you might think he had if you looked at...
I'm on record a number of places as not being a big fan of ERA. It's a pretty poor statistic in that it depends on subjective assessments of what counts as an earned run and what doesn't count as an earned run. It also depends on how well a starter's relief pitchers help him out by keeping inherited runners from scoring. It also depends on how well your fielders play defense, because even on plays where they don't make an error, they can definitely let you down. Right now, Lohse's ERA is a scary 8.92. Egads.
What are the specific contributing factors to this ERA? First off, someone instructed the Twins' scorekeeper to stop charging anyone with an error. So, Lohse has allowed exactly as many earned runs as he has unearned runs, but don't let this fool you into thinking that the defense has been fine when Lohse has been pitching. (More on this later.) As far as relief pitchers letting Lohse down, that hasn't really happened. Of the 7 runners that were left on base when he was taken out of games this season, you could have expected about 2.9 of those runners to score. The bullpen has allowed 3, so they've given him as close to league average support as possible.
But, what is the main reason that Lohse's ERA is so much higher than his FIP?
The Defense Stopped Catching The Ball
After the ball goes into play and the fielders have a chance to convert it into an out, a pitcher has little control over what happens. Mainly, a pitcher is responsible for whether or not a hitter hits a groundball, flyball, line drive, or pop up. It's been shown by many people that a defense is mainly responsible for how many of those balls get turned into outs and how many fall in for hits. A pitcher can have some effect, but it is usually pretty small and has to do with extremely weird groundball, flyball, etc. rates. We measure this with the pitcher's opponents' batting average on balls-in-play (BABIP). How has Lohse fared?
Opponents are hitting a full 56 points higher on balls in play against Lohse than they did last year, and mostly all Lohse can do is stand back and watch.
Is it Lohse's fault?
Maybe Lohse is special? Maybe he breaks the system? I don't think the evidence points in that direction. Let's look at how the defense did as a whole in allowing hits on balls in play last year compared to this year:
That gives us a difference of 61 points in batting average. So actually, Lohse's BABIP has changed less than we might have expected just by looking at the change in defense as a whole. Also, we can check what type of balls in play he has allowed:
LD% GB% FB% POP%
2005 0.19 0.46 0.28 0.08
2006 0.19 0.37 0.35 0.08
This year, Lohse has allowed fewer ground balls, but more fly balls. This is not necessarily a problem, as fly balls are converted into outs more often than ground balls and Lohse's home run rate has not gone up. In fact, this somewhat explains why Lohse's BABIP has gone up less than the team's BABIP has gone up.
Lohse doesn't deserve to be sent to AAA. He's had a bit of a rough start on the control front, with a higher than usual walk rate. However, his walk rate isn't so high that he couldn't just as easily fix it in the next two or three weeks. The real problem is that the defense hasn't been giving Lohse any support whatsoever. This Lohse is essentially the same pitcher he was last year when he was one of the best 4th starters in the league.
What about Boof? Boof's an interesting guy, and I think he could be a decent pitcher in this league. However, I think Lohse is better. The preseason PECOTA forecasts have Boof as a 5.28 ERA pitcher and Lohse as a 4.95 ERA pitcher (both assuming league average defense/relief pitching backing them up.)
Lohse was the better pitcher before the season started, and he hasn't done enough to change my mind. Bonser figures to have a higher strikeout rate, but if you're sick of Lohse's walks, Bonser figures to walk even more hitters than Lohse. Boof's minor league home run rates are also a cause for concern, at around 1.25 HR/9 over the past year or so. That's a higher home run rate than Kyle Lohse has had pitching in the major leagues against much stronger competition. Bonser might wind up working out slightly better because he'll be somewhat less likely to be victimized by the bad defense just because he'll probably allow fewer balls in play than Lohse did. Still, I just don't think that's enough to merit moving him above Lohse on the depth chart.
People will enjoy the glimmer on their shiny new toy, along with his fun-to-say first name, but I imagine it'll wear off pretty soon once they discover that Bonser is likely just as good a pitcher as Kyle Lohse, if not worse.