Well, here goes another shot at a Fanpost. I appreciate all of the patience you guys showed with my first one, and I'll try to up my game here. I've been a baseball fan since I was a kid, and I was a huge fan of Bill James back in the '80s, but I lost interest in the sport during the latter part of the Steroid Era. So the last 12 years or so of sabermetric development got past me, and I'm still catching back up.
We've all been impressed (and at least in my case, pleasantly surprised) by Jair Jurrjens' improvement this year. As of this morning, he not only leads the NL in ERA, but that lead is 59 points (over half a run!) ahead of second-place Kyle Lohse of the Cardinals. So the two big questions are: (1) what's he doing different, and (2) can he keep it up?
Let's start with the fundamental stats. Jurrjens' stats from last year are pretty representative of his career prior to 2011, so we'll use that as a basis for comparison. Last year JJ pitched 116.1 innings, roughly 120; this year so far he's pitched 79 innings, or roughly 80, so this is a good place to make projects and compare to last year. The first thing that jumps out is walks. So far this year he has walked 11, so when he reaches the same number of innings he pitched last year, it projects to 18 walks. Last year he actually walked 42. Huge improvement there, obviously. And it shows up in his WHIP: 1.00 so far this year vs. 1.39 last year.
Dave Allen has a post up at Fangraphs analyzing JJ's improved walk rate. One thing he found was that last year, batters who worked to a 3-ball count on JJ walked nearly half the time, 46%. This year, it's 28%. Allen produced pitch charts for last year and this year looking at fastballs JJ has thrown on three-ball counts. Last year, against RH batters, he grooved a bunch of them and most were swung on. However, against LH batters, JJ was all over the place and lot of his three-ball fastballs were nowhere close. Sure enough, when we look at last year's status, 12.7% of LHers who faced JJ walked. This year: 6.9%. There's a very noticeable difference when you look at the pitch charts.
The second thing is extra-base hits. Last year, JJ surrendered 27 doubles, 9 triples, and 13 home runs. This year, he currently is at 10, 3, and 4 respectively. Projecting these to the same number of innings as last year, we get 15 (vs. 27), 5 (vs. 9), and 6 (vs. 13). This shows up in opponent's slugging percentages; .458 last year vs. .329 this year, and is a big contributor to opponent OPS being nearly 200 points lower this year even though the total number of hits projects out to about the same (103 vs. 120 last year).
So how is he doing all this? We all know that JJ has actually lost (or given up) a bit of velocity on his fastball. Normally this would not be a good thing, but if a pitcher is over-throwing, backing off a bit in exchange for much better location might be a good trade. Does the available data support this? Maybe; I'm not totally convinced. JJ's ground ball percentage is up a bit from last year (44% vs. 39%) but last year was below his career average, and this year's number is more in line with it. His BABIP is anomalously low, at .260. That may be a warning sign, but consider this: his home runs per fly ball percentage is at 4.8%, about half of last year and significantly below his career number of 7.0%.
Now, conventional sabermetric theory holds that HR/FB% is an independent variable; the pitcher cannot control it and so a pitcher who improves this number is merely lucky. I disagree. I think that there's a big difference between a pitcher whose fly balls are mostly popups and cans-of-corn to the outfield, vs. a pitcher who dives up a lot of hard hit line drives. I think the HR/FB% reflects this, and I also think that this year JJ has gone from being more the latter type of pitcher to more the former. I hold that the decrease in slugging and rate of extra-base hits against him demonstrates this. How is he doing it? Here's a clue. Remember when we said above that JJ grooved a bunch of three-ball fastballs to RH hitters last year? He's not doing that this year. Most of those three-ball fastballs to RHers have been on he outside third, and there's nothing in the center square. This further supports that the decrease in slugging is not just luck. His command really is better, an/or he has more confidence to not give in to righthanders on a batter's count.
One cautionary note. Mike Podhorzer at Fangraphcs points out that JJ 's ERA is nearly two runs ahead of his current xFIP. Among other things, he thinks JJ's current walk rate is unsustainable and will regress to his career average. It may be true that JJ's current ERA is somewhat lucky, but even if it regressed by a whole run, JJ will still be among the league leaders. And if JJ's approach to pitching has really changed, I see no reason why his current walk rate should not be sustainable.