I've been weirdly obsessed with this for a while now, and I feel like it gets lost amid the angst about the terribleness of the season and his contract negotiations and everything else. I feel like it needs attention, because I've heard people elsewhere (not on this site) claim that Lester's not an ace, and more of a #2 starter. Those people are wrong.
From 2008-2010, Jon Lester was one of the 10 best pitchers in baseball. From 2011-2013, he was less than that. Now, he's having a great year. He currently has a career-best 65 ERA- and FIP-, and while those numbers are likely to regress some in the second half of the season, so far he's been performing at his best. Mark Buehrle and Josh Beckett are also having great years, but no one is going to suggest those guys are at their best. So what's special about Lester? What's going on with him?
To start with, his walk rate is a career-best 5.5%. His walk rate's been improving for a few years now, even during his otherwise disastrous 2012. Perhaps more importantly, his strikeout rate currently sits at 25.5%, his highest mark since 2010. His career high strikeout rate is 26.7%, which he achieved in 2009. His strikeout rates were in decline from 2011-2013, and this contributed to the difficulties he had. They weren't the only cause, but they were definitely a part of it.
So why did he lose his strikeouts? Velocity, right? He's getting older and doesn't throw as hard as he used to, and it's easier for hitters to catch up to his heater. Simple enough, isn't it? Let's check the excellent Brooks Baseball to see:
See! it's right there. He's losing velocity, as pitchers do when they age, and that's why he lost his strikeouts. But now he's getting strikeouts again, but his velocity is not back, which means something is up. Maybe he's getting crafty, throwing his fastball less, and using other pitches more?
No! he's throwing them more, at the highest rate he has since 2007! This doesn't fit the narrative at all! We need to go deeper to find the answer. Let's look at the whiff rates on his pitches.
For those that don't know, whiff rates measure the rate of swinging strikes per pitches thrown. They're a good predictor of strikeouts, because most strikeouts happen when the batter swings and misses. A higher whiff rate means a pitch is harder to hit.
Now we're getting somewhere! These two charts, taken together, tell the story of Jon Lester. The velocity on his fastball isn't the problem - the swinging strike rate on it has actually been going up the past couple years! It's not as good as it was in 2009 (8.8% vs 7.24%), but it's pretty close. The real story of his strikeouts has to do with his off-speed pitches. In 2009-10, his curveball and cutter were great, producing whiff rates of 14.7% and 15.7%. The average whiff rates for those types of pitches is closer to 10%. Lester's problems began when he struggled with his mechanics, and his stuff became less effective. His curveball's swinging strike rate dropped to 9.93% in 2011. In response, he started throwing his cutter way more, and using his curve less. However, he began to lose effectiveness on his cutter, too - its whiff rate dropped to 12.99% in 2012 down to 11.19% in 2013. It's crept back up this year to 13.47%, which is below his peak, but solidly above average. His curveball, though, has been greatly improved, and now sits at a career high 16.79%. Some of this is probably a spike from his excellent start against the White Sox, where he used the curve heavily, but it's safe to say the curve is a weapon for him again, and that gives him three pitches to challenge batters with.
It's also interesting to note that he's decreased the usage of his sinker and changeup. The sinker used to get a decent amount of whiffs, but it's been steadily declining, so that's part of it. It was also hammered hard in 2013 (over .600 slugging against), so that might be why he's not using it as much. The changeup seems to get a great swinging strike rate, but he's only thrown 79 this year, so we're looking at a limited sample size. The pitch has been hit hard when he's thrown it, with a .375 batting average against and .500 slugging against, although, again, this is a limited sample. He might just not feel as confident in it. It's still a good fourth pitch to give batters a different look and complement his main weapons of the fastball/cutter/curve. His reduced use of the sinker means he's getting fewer ground balls, but it's an acceptable tradeoff for getting his strikeouts back.
Of course, this isn't the whole story, there are other factors as well - his pitch location, sequencing, and the framing abilities of David Ross are also part of the story, but this is probably the most important part. It explains why his strikeouts were gone, and now they're back.
So why do I say he's at his best? Well, really, he's been this good for a year now. He was terrible in the first half of 2013, as several blowup starts pushed his ERA to 4.58, with a 4.15 FIP to go with it. He had an awful 19.1 K% and 8.4 BB%, which corresponds to a roughly average strikeout rate for a starter and a below-average walk rate. Not a good combination. However, he rebounded enormously in the second half of the season, posting a 2.57 ERA and 2.77 FIP en route to a dominant performance in the postseason. His K% only went up to 20.3%, but his BB% dropped to just 6%. He was succeeding more by avoiding giving up home runs, but it was a definite improvement for a pitcher that previously seemed to be in freefall. We can see, too, that it was at this point he began changing his pitch mix:
more fastballs and cutters, far fewer changeups and sinkers. He experimented until he found a mix that works for him, and has continued to use it to great success this year. 2014 Jon Lester is nearly the same as 2013 playoffs Jon Lester.
In fact, he's been performing at a truly elite level. Fangraphs lets you organize their leaderboards by performance over the past calendar year. When you do this to their pitching leaderboards, you get the following:
Incredible. By fWAR, Jon Lester has been the second-most valuable pitcher in baseball over the last year. This stretch would be better than any single season of his full career so far. It's reminiscent of peak Cliff Lee in terms of dominance. Of course, fWAR is a counting stat, which penalizes players who miss time, like Kershaw did. Jon Lester isn't better than Kershaw, because no one is better than Kershaw, but he's been extremely productive in this time. To give another perspective, here's how he ranks in some other advanced stats:
ERA-: Tied for 3rd.
FIP-: Tied for 3rd.
xFIP-: 22nd (what an...interesting list)
So what's the point of all these stats? The point is this: for a year now, Jon Lester has been pitching like an ace. He's having the best run of his career, and it's not a mirage. His strikeouts are back, and his walks are down. I would argue that he's currently one of the 10 best active pitchers in MLB again. Anyone who says he's not an ace simply isn't paying attention. He doesn't have the amazing stuff that some other pitchers have, but in terms of performance he's been one of the best. This is a set of arbitrary endpoints that's favorable to him, but it's a good way of showing how he's improved.
I don't know how much longer Lester will keep performing at this level - he's had problems with his mechanics before, they could always creep up again. He had a good first half in 2010, only to slip a little in the second half. I don't know if this is his last year in a Red Sox uniform. But I know that right now, he's the best he's ever been. And I think that goes a little under-appreciated because he got stuck with the labels of "inconsistent" and "not an ace" at some point in his career, and while that was true for a while, it's not right now. Right now he resembles the younger version of himself, when he was one of the game's best.
So if you read all this, first of all: thank you for reading all this, and congratulations. Secondly, be sure to appreciate every remaining Jon Lester start this year, because he's a true great pitcher, and this may be the last time you'll get to enjoy him like this. I hope that's not the case, but I don't know, so here's to however long it lasts.