For a guy who's been a model of consistency as far as MLB starting pitchers go for a decade and half, it's been a surprisingly up-and-down start to the year for Mark Buehrle. His first three starts were blowouts where he seemed to just pitch to contact to get his six innings and the W. That was followed by two poor starts the last week of April, when reports of potential injury concerns popped up. Back in division play, he turned in two good, but uncharacteristically short starts where he was held under 80 pitches. His two most recent starts haven't been as good, but it appears whatever cautionary measures he was under no longer apply, as he's worked into the 8th in both and gone to 111 pitches.
So how to make sense of all this in terms of what can be expected going forward? Let's start by stacking this year up against the last couple as has been done throughout this series:
Buehrle's ERA sits at an inflated 5.13, perfectly matching his FIP with both well over a run above last year. The biggest reason for that is all the long balls he's giving up, with nine home runs allowed in nine starts. He's keeping the ball on the ground at a normal rate, but when he does give up balls in the air, a disproportionate number of them -- 14% -- are leaving the park, with league average at 10-11%. Fortunately, as we know, this tends to even out over time. In a karmic season, this year is basically payback for last year, when Buehrle was greatly assisted by a 3% HR/FB on the same date. Curiously, this isn't even a Rogers Centre problem, as he's given up six home runs on the road (17% HR/FB) versus only three at home (10% HR/FB).
The other significant factor is that Buehrle's strikeout rate has tumbled by 25%, from about 15% in his first two years as a Blue Jay to just over 11%. This type of "fall off a cliff" can be a red flag that a pitcher is experiencing a fundamental decline in skill, which would not be unforeseen for a 35 year old pitcher with over 3,000 MLB innings. However, looking at the pitchf/x data at Brooks Baseball, there's doesn't appear to be a decline in stuff, which would usually be an even better indication of fundamental decline.
What's even more unusual is that Buehrle's strikeout rate actually has spiked the last three seasons, from the 12% range in his last three seasons in Chicago to the 15% range from 2012 to 2014. 2012 could be explained by going to the NL East, with weaker opposition and some pitchers hitting, but it stayed elevated in back in the AL, and the AL East at that. And it's not like his stuff got better, or he found a way to miss a lot more bats - most of the increase was due to more strikeouts looking.
So far this year, Buerhle has missed significantly fewer bats this year, across the board count wise, and that's the root cause. Whereas he used to induce swinging strikes about 7% of the time, he's down to 5% in 2015, and that's driven his contact rate from the mid-80s to just under 90%. It could well be this is related to the health problems, but unless it improves, the strikeouts should not be expected to bounceback.
There's one caveat to this. As I mentioned at the outset, in Buerhle's first three starts the Jays put the game away early, as in only 5 of 18 innings did Buerhle start the inning with less than a four run lead. In that situation, his job is basically to eat innings, let them put the ball in play and it's alright if they do a little damage as long as the big innings are avoided. In those 13 innings with a big lead, Buehrle struck out just 4 of 58 batters (7%). In all other innings this year -- all of which were within 3 runs -- Buerhle's struck out 23 of 180, or 13%. This may sound like grasping at straws, but even in such small samples, the difference is highly statistically significant. So maybe Buehrle's strikeout rate is unduly influenced by him "pitching to the score" so much in the early going.
Going back to the top, there's two other things hurting Buehrle some. His walk rate, though still very good, is up, and this appears to be part of a trend, which fits with normal aging expectations. His BABIP is also up, and while that too appears to be a longer term trend, there's a ton of other variables that affect BABIP (whereas walk rate is mostly about the pitcher). We can likely expect a little relief there the rest of the way.
Overall then, based on what we've seen in the early going, I'd expect Buehrle to continue being Buehrle, albeit probably with a reduced strikeout, in the 11 to 13% range rather than 14-15%, and allowing a few more free passes than in past years. The X-factor might be his health. It appears he's back to normal usage patterns after a stretch of abbreviated outings, but I'd imagine at this point is in his career he's not frequently going to be 100%.