Boston Red Sox: How does the rotation look now?
The Boston Red Sox rotation has shown some chinks in the armor lately. Was the early season success a mirage? Is this latest perceived swoon representative? We’ll use some advanced metrics to dig in.
It seems like ages since the Boston Red Sox rotation looked to be among the best in baseball. Rick Porcello has shown his warts… again. Drew Pomeranz looks like his arm might fall off. David Price has struggled with some minor health issues. And even Chris Sale has been scuffling lately. So where do they stand after a bit more than a third of the season? Let’s take a look!
There are a number metrics we will use to examine the staff here, and none of them are the traditional wins or ERA. The reason for that is that we want to get at how good they are, not how good their results are. ERA depends heavily on defense and some luck.
Wins require the offense scoring runs. Neither is something that digs into how well a pitcher has performed all that well. A terrible defense will allow more balls in play to poke through the infield or fall into the gaps. A team with a terrible lineup might saddle its starter with losses on nights when they go 7 IP allowing just two runs. So what are we going to use?
Time to go to fWAR.
Overall, the staff ranks 5th in fWAR. I like fWAR more than rWAR for pitchers because it isn’t based on runs allowed. It’s based on FIP. The concept behind FIP is to strip away contextual noise as much as possible, leaving you with as clean a look you can get at what a pitcher directly controls. That means strikeouts, walks, and home runs for the most part. So we’ll use that here.
The club has amassed six fWAR to date, putting them behind the Indians (6.1), Phillies (6.7), Nationals (7.6) and Astros (9.5). Putting aside just how bonkers that 9.5 fWAR from the Astros is, the Red Sox rotation certainly looks good enough.
The Yankees, their closest division rival, have 4.7 fWAR. The next closest are the Rays with 3.5, good for 13th in baseball. If the goal this season is to win the division and avoid the play-in game, the rotation is doing its part in getting them there. At least by this metric…
Speaking of FIP.
Fielding Independent Pitching is a method of focusing on what a pitcher can control. Essentially, it looks at the three true outcomes and ignores balls in play. While the three true outcomes aren’t truly 100% in the pitcher’s control, they are the things a pitcher can control most. Variables like catcher framing, weather, park dimensions, and umpire accuracy can all impact these events. But for the most part, FIP is better at predicting future success than ERA. That doesn’t mean it’s a full replacement, however. One of the best ways to use FIP is to compare it to ERA and then try to explain the difference.
Where do the Red Sox starters rank in FIP? They drop down one spot to 6th, with a 3.59. How does that compare to their ERA? It’s a bit better. Their ERA of 3.79 ranks 9th in baseball, so perhaps there is a reason to expect a bit of improvement as we move forward. The Astros lead baseball in both metrics, by the way.
Then there’s FIP’s little brother, xFIP.
What do you get when you take a context neutral stat like FIP and decide you need it to be even more context-neutral You get xFIP. The adjustment made from FIP to xFIP is pretty simple. It takes the actual home run rate of the pitcher or pitchers and replaces it with the league average home run rate. The reason for this is that home runs per fly ball can be a bit fluky from year to year.
Plus, we start seeing those pesky variables that make the three true outcomes not quite so true popping up. That home run right down the line in right field at Fenway Park? It’s a pop out or maybe a double in Tampa — a lazy pop fly that scrapes the Green Monster? Easy out in Toronto. So enter xFIP to strip away even more of that stuff a pitcher has no control over. Like FIP, you want to compare it to other things. Namely, FIP and ERA. It actually might help answer why there’s a difference between them.
In this case, the Red Sox rank 8th in baseball in xFIP with a 3.77. Looks pretty similar to their FIP, so we can probably surmise that they haven’t had a massive amount of luck (one way or the other) on home runs so far. That backs up the guess we took above about them maybe seeing some improvement in their actual results (ERA).
And finally, there is SIERA.
There’s one more stat out there that tries to do what FIP and xFIP do, but it takes a slightly different path to get there. SIERA, or skill independent ERA, doesn’t ignore balls in play. But it does try to get into the nuts and bolts of results on balls in play. Here’s a link to the Fangraphs write up on the metric, and a quote from that page:
“SIERA adds in complexity in an attempt to more accurately model what makes a pitcher successful. SIERA doesn’t ignore balls in play, but attempts to explain why certain pitchers are more successful at limiting hits and preventing runs. This is the strength of SIERA; while it is only slightly more predictive than xFIP, SIERA tells us more about the how and why of pitching.”
Essentially, strikeouts are good, walks are bad, and higher ground ball rates lead to more outs on balls in play. So how do the Red Sox look by SIERA? They come in at 4th in baseball with a 3.62.
Another indication that their 3.77 ERA might come down a bit. Of course, none of these metrics are suggesting a ton of variation between the quality of their outings and the results they are seeing. This is likely a top 5 or 6 rotation in the game, but they aren’t a threat to unseat the Astros at the top of the hill.
What else can we look at?
If you want to know how the difference between their ERA and FIP ranks in baseball, there’s always E-F. Here the Red Sox Rotation is 9th in baseball at 0.20, meaning only eight teams have a larger disparity. None of those teams are ahead of the Red Sox in any of the four metrics we’ve looked at so far. The Mets aren’t too far behind and do slot in with a slightly higher E-F at 0.30.
We can also look at the kinds of contact being allowed. Currently, the Red Sox have a 42.1% ground ball rate, 21st highest in baseball. So they are allowing plenty of fly balls. The good news is, few of them are line drives.
Their 18.5% line drive rate is the third lowest in the game. That matches up well with their league-leading soft contact percentage of 22.4%. So yes, they are allowing more balls in play in the air, but they aren’t allowing hard contact on them all that often.
That gets at the description in SIERA when discussing ground balls and how they lead to outs more than fly balls. If the contact in the air is of the soft variety, we’ll see plenty of outs there. And with three excellent defensive outfielders in Andrew Benintendi, Jackie Bradley Jr., and Mookie Betts, that will be true even on a fair amount of the hard contact.
And here’s the other thing. The Red Sox have the second lowest pull percentage in baseball at 39%. That’s important since it also fuels the lower hard contact rate on balls allowed in the air.
How do balls in play in the air break down league-wide?
So far this season, MLB has a 401 wRC+ on balls in the air to the pull side. That’s 301% better than league average. Allowing the other teams to put the ball in the air to the pull side is bad. Very bad. If we compare that to up the middle contact in the air, we see a 168 league-wide. Opposite field? Just a 95 wRC+.
So the Red Sox keeping hitters from going to the pull side is allowing them to succeed despite a higher rate of balls allowed in the air. It’s one of the reasons why their line drive rate is so low.
That’s a pretty good indication that what they are doing is sustainable. And if they can keep this up, they have as good a shot as anyone of succeeding in the playoffs. This isn’t the best rotation in baseball. Not even close.
Next: Sox names to look for in the 2018 MLB draft
But it does appear that warts and all, it is good enough for this team to win the division and make a run in the postseason. With the offense looking like one of the best in the game, it will come down to the bullpen. And while the pen may inspire more questions than the rotation does, that’s a look for another day.