With Britton, Yanks 'pen may be one of best ever

The Yankees didn't needto go getZach Britton, and that's really the entire point. We expected way back in January that this was going to be baseball's best bullpen, and that's exactly what happened. Just look at all of the different metrics that the Yankees relievers are No. 1 in.
They're also first in fastball velocity, at 95.3 mph, despite throwing the fifth-fewest fastballs, just 50 percent. (That's important. We'll get back to that.)
That is just so many things to be good at, to the point that their Triple-A team is flush with relievers who should probably be in the big leagues but for lack of roster space, and now they've gone out and added a reliever who was once considered so elite that there was a groundswell of support to get him into the Cy Young conversation back in 2016. They've been so good without Britton. What in the world are they going to be with him?

• Listen: Petriello, Meyers discuss Britton joining Yankees bullpen
Before we can answer that, we need to express how good they've been, historically, just like we did over the winter. Let's acknowledge that there's not really a perfect way to rank bullpens, especially back through the years, as usage has continued to change. Let's not be held up by the lack of perfect options and go with the best ones we've got. One way to do that is to look at Fielding Independent Pitching, which looks at strikeouts, walks and home runs, and puts it on an ERA-like scale. It ignores quality of contact, but in the pre-Statcast™ era, there's only so much that can be done there.
There have been nearly 2,200 team seasons since the live-ball era began in 1920. We'll look at each bullpen's FIP mark and compare it to league average, expressed as "percentage points above average." Would you be interested to know that the Yankees have two of the top six seasons?
Best relief FIP compared to MLB average, 1920-2018
32 points above average -- 2003 Dodgers
32 points above average -- 1964 Reds
30 points above average -- 2018 Yankees
29 points above average -- 2018 Astros
27 points above average -- 2017 Indians
26 points above average -- 2017 Yankees
You can do the same for ERA, where the Yankees relievers and their 2.75 ERA is making them 35 points better than the 4.03 league average, and one of the Top 10 groups since 1969.
That's all without Britton. Can we expect more with him?
Here's the first thing to know: Britton may not be the stud he once was, but there's still a lot to like here. It's easy to look at his 3.45 ERA, his 21 percent strikeout rate and his 16 percent walk rate, and note that they're all well below the numbers he put up in his 2014-16 glory days, but it's also not really a good indicator of what the Yankees can expect going forward. Unsurprisingly, Britton needed some time to shake off the rust caused by his offseason Achilles tear. While that's caused his annual velocity average to decline, it's been much better in July.

So, too, have his results. In June, Britton allowed six runs in 8 2/3 innings (6.23 ERA), collecting an 18 percent strikeout rate and a 54 percent grounder rate. In July, he's allowed zero runs in seven innings, upping the strikeout rate to 25 percent, and the grounder rate to 80 percent. If he's not necessarily "back," he certainly looks like he can still be a capable above-average reliever.
Just take a look at their current bullpen, understanding that someone is going to have to be removed in order to get Britton on the roster. (Our best guess is a disabled-list stint for a certain lefty closer with a sore knee.)
L -- Aroldis Chapman
L -- Britton
L -- Chasen Shreve
R -- Dellin Betances
R -- Chad Green
R -- Adam Warren
R -- David Robertson
R -- A.J. Cole
R -- Jonathan Holder
That's an incredible list of names. Seven of those eight non-Britton relievers have been above-average pitchers this year, at least in terms of results, and even the much-maligned Shreve has been much better lately, striking out 12 while allowing only two runs in his last 10 games.

There's plenty of stars here, obviously. You know all about Chapman, Robertson, Green, and the nice recovery of Betances. But really, this is a story about depth. Take Cole, for example, a former Nationals top prospect who had a 5.32 ERA in parts of four seasons for Washington. Though he won the fifth starter job with the Nats out of camp this year, they cut him loose after two poor starts, allowing the Yankees to pick him up for mere "cash considerations."
With the Yankees, he's been outstanding working in relief. Cole has an 0.87 ERA in 20 2/3 innings in pinstripes, striking out 26 against only six walks, and he's done it buying into the "Yankee way." Cole has doubled his slider use from what he had done with Washington and greatly diminished his fastball use.

Look deeper, to Triple-A Scranton/Wilkes-Barre. Remember how dominant Tommy Kahnle was last year, after he was acquired from the White Sox with Robertson and Todd Frazier? He struck out 36 in 26 2/3 innings, but he's spent most of 2018 in the Minors or on the disabled list after walking 10 hitters in his first eight games. If you haven't been watching International League baseball, you might not have noticed that it sure looks like he's dealing again: In 17 innings since June 1, he's allowed a .150/.250/.233 line, to go with a 2.12 ERA and 27 strikeouts.
Look at Giovanny Gallegos, who led all of Triple-A last year with a 40.9 percent strikeout rate and has followed it up with a 35 percent mark this year and can't get a real opportunity. Look at prospect J.P. Feyereisen, part of 2016's Andrew Millertrade, who has a 1.93 ERA in Scranton/Wilkes-Barre and nearly a strikeout per inning. There's just not enough room for all of these guys, not until rosters expand in September, anyway.
Then again, teams don't think about pitching staffs the way they used to. In the Yankees rotation, Luis Severino is an ace, while CC Sabathia and Masahiro Tanaka have their moments, but they're looking at an especially weak starting-pitching market before the non-waiver Trade Deadline. One way around that is to make a very, very good bullpen even deeper. In the postseason, it will allow them to pull ineffective starters just as quickly as they need.
They didn't need Britton, not really. They made sure that the Red Sox didn't get him, though. You can bet they'll notice during the 10 remaining head-to-head matchups the two longtime rivals share.