Unsolved Mysteries: Stephen Strasburg
In all of my posts I look to take some statistics, present them in a logical manner and share my own conclusion from these statistics. This has been a tried and true formula that has been highly effective. However, today's topic has left me without a conclusion and you'll hopefully soon see why. So instead we'll go a bit more behind the scenes as I take you through my research process for this post. To start I knew I wanted to write about Stephen Strasburg. He's been a hot topic among Nats fans since the Opening Day and no one can quite get a read on him. By many measures he's been one of the best pitchers in baseball, but by the most important measure, runs allowed, he's been merely average. How is it that someone with such great stuff and peripherals is producing such pedestrian results? This is what I aimed to find out.
This process started on the macro level. Strasburg currently possess a 2.73 FIP and a 3.39 ERA. Right off the bat we can see that there is something wrong here, so let's dive a little deeper. Strasburg has a sterling strikeout rate at 28.2% and the best walk rate of his career at just 5.3%. Awesome, looking good so far. On the other hand he has a BABIP of .341 and a strand rate of 71.7%. And here's where we're seeing the difference between his FIP and ERA. The lazy analyst would stop here, chalk it up to luck and grab another beer from the fridge. But we're better than that, let's look into some possible causes for such poor rates.
The first check is to see whether batters are just hitting the ball harder against him. The first thing we look at is his groundball to flyball ratio, which is currently 1.48, exactly his career rate. So there isn't much of an issue there. The next thing we can check is his home run to fly ball ratio, which is at 11.4%, essentially in line with his 2012 and 2013 ratios of 11.5% and 11.1% respectively. So on the surface it doesn't seem like opposing hitters are getting better contact against Strasburg than they have previously, but we can dig a bit deeper here.
Mark Simon of ESPN Stats & Info tracks a stat called hard-hit rate, which tracks the percentage of at-bats that end in a hard hit ball for both hitters and pitchers, but we're only concerned about the pitchers here. Here's his latest update for pitchers who have given up the least hard-hit balls this season.
As you can see, Strasburg ranks 32nd among starting pitchers in giving up the least hard hit balls this season. So this doesn't seem to be an overall issue for him. Let's move on.
Much was made early in the season when Strasburg had trouble with his fastball velocity in his opening day start against the Mets and we know that a decrease in average fastball velocity affects pitcher performance, so let's look at that next. In fact, Strasburg's average fastball velocity is down by 0.7 miles per hour compared to 2013 according to PITCHF/x, which could lead to problems. However, he seems to have realized this, as his fastball usage has also dropped by a little over two percent according to Fangraphs. And opposing batters are swinging at it just as much (46% swing rate in 2014, 46.6% career) and aren't making much more contact (86.8% contact rate in 2014, 85.3% career). Not to mention that Strasburg's slightly slower fastball is still sixth fastest among qualified starters. It's not like he's throwing beach balls out there.
Let's try another angle of attack, mistake pitches. It seems like an easy solution. A guy who overall puts up very good numbers, but once or twice just grooves a pitch that leads to runs and a loss. However, Strasburg's home runs allowed per nine innings is 0.83, right in between his 2012 (0.85) and 2013 (0.79) rates. So it already isn't looking good for this theory, but let's press on. By using Baseball Savant's PITCHF/x tool we can get the number of pitches a pitcher has thrown into a specific area of the strike zone as seen in the photo below.
For our purposes, let's define mistake pitches as ones thrown right over the middle of a batter's strike zone, sections 4, 5 and 6. It stands to reason that a player who throws a higher percentage of his total pitches in these zones is throwing more mistakes as it's not often that a pitcher wants to throw a pitch over the middle. Running this we find that the average among pitchers who have thrown at least 1000 pitches this year is 15.4% mistakes. Strasburg checks in at 15.39%, right at the group average and 81st among the 166 pitchers making up this group. So he doesn't seem to be making more mistake pitches than the average pitcher would. While average isn't great, it doesn't explain such a large difference between ERA and FIP.
The last thing we can look at is how Strasburg performs with runners on base. Particularly, whether he is susceptible to allowing hits in bunches, which would allow for more runs to score than would be indicated by his peripheral statistics. For this we can take the number of hits allowed by a pitcher with men on base as a percentage of their total number of hits allowed. It's not a perfect measure, but it should give us a good idea if something's not right. In this case I ran the numbers for all qualified pitchers. The group average is 41% of hits coming with men on base. For Strasburg that number is 42%, barely above the group average. Again, not something that indicates the need for concern.
By nearly all respects Strasburg is having the best season of his career. Opposing batters are chasing more pitches (36% O-Swing% in 2014, 31.9% career) and giving him more strikes (11.9% swinging strike rate in 2014, 11.3% career). He's even throwing more first pitch strikes than ever before with a 64.9% first pitch strike rate, the highest of his career outside of his short stint in 2011. And yet there is some disconnect between all of that and the Luck Dragons BABIP and LOB%. While you don't want to just reject a high BABIP and low LOB% out of hand, in this case I believe it to probably be warranted. If Strasburg continues to pitch the way he has all season, I think he should see his runs against results come more into line with what his FIP and SIERA predict he should be doing. And if that turns out to be the case, look out National League.