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Searching the relief market for diamonds in the rough

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An analytical approach to pitching can identify potential bargain grabs in free agency.

Photo by Lisa Blumenfeld/Getty Images

As any tactful owner would tell you, the tail end of fantasy baseball drafts are frequently spent on de facto lottery tickets. Less volatile players are passed up for intriguing but unproven rookies and prototypical "boom-or-bust" selections. The cost-benefit analysis behind these picks is simple: each choice presents less overall risk than the prior selection. A first round superstar who disappoints could sink a virtual team's entire season, but a late-round gamble who fizzles out can simply be swapped out through waivers void of any serious ramifications. Owners who take a chance on these fliers are more likely to hit the jackpot on players that yield a major return on investment. Even if you don't expect any specific player to break out, probability says at least one hidden gem will emerge at a bargain price.

The sheer volatility of relief pitchers in particular was a key focal point of Ben Godar's article entitled The Cardinals should build a bullpen through quantity, not quality. Said the Ringer's Ben Lindbergh on MLB Network after the Rockies inked Wade Davis to a three year, $52 million pact:

It's easy for me to sit here and play GM behind the table and say 'Go get the next guy who has that sort of stuff,' but every single year we see teams unearth people like that who pitch just as well but don't come with that kind of contract.

Of course, for every Pat Neshek and Seung Hwan Oh there will be busts whose contributions to the big league club prove negligible. Even so, what does a team oozing with payroll flexibility have to lose by swinging for the fences on a few cheap bullpen arms?

When the World Series champion Astros snagged Charlie Morton, their second most valuable pitcher in 2017, for just two years and $14 million last winter, it was the type of move that encapsulated modern day baseball operations. At the time of the signing, the righty owned a career ERA of 4.54 and a 4.74 mark over the previous two seasons.

Houston, however, saw things a little differently. More precise metrics like DRA, SIERA, and xFIP suggested that Morton was a better pitcher than the back of his baseball card would indicate. More importantly–after all, every team has developed projection models superior to any publicly available stats–Jeff Luhnow's brain trust spotted a pitcher with an elite curveball spinning 3,000 times a minute to pair with above average fastball velocity. The Astros had access to the same haystack of information as everybody else, but they knew where to look to find the needle.


Fastball spin rate, measured in revolutions per minute (RPM), correlates strongly with swinging strikes and in turn strikeouts. While higher spin fastballs generally have higher velocity, the two aren't dependent upon one another. Blue Jays starter Marco Estrada ranked 112th among qualified pitchers with an average fastball velocity of 88.1 MPH in 2016, but the pitch's 2,401 RPM spin rate (8th best) carried him all the way to his first ever All-Star appearance.

Driveline Baseball created a metric called Bauer Units (named after one of the company's most notable clients) to quantify a fastball's effectiveness based on its velocity and spin rate. A 2,400 RPM fourseamer at 100 MPH doesn't throw hitters off balance the same way a 2,400 RPM pitch clocked at 90 MPH does. For the sake of context, I have converted all Bauer Units into BU+, where 100 is league average. By my count, 11 free agent relievers who posted an above average BU+ in 2017 remain unsigned.

Free agent relievers with above average BU+

Name Pitches Avg. Spin Rate Avg. Velocity Bauer Units BU+
Name Pitches Avg. Spin Rate Avg. Velocity Bauer Units BU+
Andrew Bailey 26 2715 90.8 29.9 123.6
Koji Uehara 419 2367 87 27.2 112.4
Sergio Romo 168 2292 86.4 26.5 109.6
Bud Norris 265 2420 94.1 25.7 106.3
Jesse Chavez 885 2333 91.1 25.6 105.8
Jason Grilli 484 2361 92.8 25.4 105.2
Tyler Clippard 421 2284 90.9 25.1 103.8
Blaine Boyer 276 2360 94.1 25.1 103.7
Greg Holland 385 2297 93.4 24.6 101.6
Trevor Cahill 37 2260 92 24.6 101.5
Seung Hwan Oh 635 2262 92.9 24.3 100.6

Andrew Bailey is a noted spin rate champion, but the shoulder issues that sidelined him in the past prematurely ended his 2017 campaign. With a track record of well above average cutter and curveball spin rates as well, he could be an interesting minor league free agent add if he can prove that his shoulder has recovered. (The 33-year-old's declining velocity certainly doesn't elicit confidence.) The early returns, albeit in a minuscule sample size, on the lower arm slot he tinkered with last season were positive, plus at the very worst he would provide minor league depth at virtually no cost.

Checking in with the second highest spin rate on the list is Bud Norris, who fully transitioned to the bullpen last year after signing a minor league deal with the Angels. Norris was excellent in the first half with a 2.23/2.96/3.21 ERA/FIP/xFIP, however those numbers swelled to 7.01/5.22/4.28 after the break, essentially killing any hopes of landing a lucrative contract this offseason. Led by a robust 3.66 xFIP and 3.60 SIERA in 2017, Norris is one of the Steamer projections' favorite available targets with a 3.90 ERA projection for 2018. On a one or two year deal, he would give the Cardinals another right-hander to help bridge the gap to Luke Gregerson in the ninth inning.

Spin rate can also shape the downward movement and groundball rate of curveballs, as evidenced by the aforementioned Morton. (90% of his curveballs that were put in play were kept on the ground in 2016, the year before the Astros signed him.) The average curveball spin rate last season was exactly 2,500 RPM.

Free agent relievers with above average curveball spin rate

Name Pitches Avg. Spin Rate
Name Pitches Avg. Spin Rate
Trevor Cahill 331 2926 RPM
Andrew Bailey 3 2764 RPM
Shae Simmons 28 2727 RPM
Jorge De La Rosa 45 2621 RPM
Jesse Chavez 185 2592 RPM
Seung Hwan Oh 19 2534 RPM

Here we find Bailey again in addition to Trevor Cahill. The wrinkle with the latter is that according to Quality of Pitch Baseball, his curve grades out in just the 17th percentile despite well above average movement due to its paltry location, which ranks in the second percentile. A metric called Quality of Pitch Average (QOPA) prefers Cahill's sinker and changeup, although the sinker only finished in the sixth percentile for location. If Cahill is insistent on getting another crack at the starting rotation, however, St. Louis may not be the best place for him for him to iron out his command issues. He has former-starter-turned-dynamic-reliever potential, but taking that next step by limiting his walk rate is no simple task.

The average slider in 2017 had a spin rate of 2364 RPM, a figure that eight free agent relievers eclipsed.

Free agent relievers with above average slider spin rate

Name Pitches Avg. Spin Rate
Name Pitches Avg. Spin Rate
Sergio Romo 488 2895 RPM
Jason Grilli 262 2674 RPM
Bud Norris 188 2662 RPM
Zac Rosscup 52 2564 RPM
Blaine Boyer 244 2432 RPM
Peter Moylan 422 2415 RPM
Jesse Chavez 348 2393 RPM
Joaquin Benoit 108 2393 RPM

Sergio Romo, who also has the third highest BU+ rating on his fourseamer, leads the pack with a slider just shy of 2,900 RPM. While QOPA as a whole is down on Romo–docking him primarily for his low velocity–his slider places in the 95th percentile for late break, 98th percentile for horizontal movement, and 60th percentile for location; his fourseam fastball is in the 98th, 89th, and 88th percentiles, respectively. The Steamer projections peg Romo for a 4.31 ERA in 2018 while ZiPS is much more bullish at 3.88.

Joining Romo atop the free agent slider leaderboards are Norris and Peter Moylan, who QOPA and Baseball Prospectus' Deserved Run Average (DRA) metric raved about last year. QOPA put Moylan's 2017 season in the 96th percentile overall with his slider in the 95th percentile and his fastball in the 99th thanks to superb late break, horizontal movement, and location. Meanwhile, his DRA- of 53.6 far exceeded the league average of 100.

The catch with Moylan is his extreme lefty/righty splits. His wOBA and expected wOBA versus righties in 2017 were .224 and .240, respectively. Against lefties, on the other hand, they ballooned to .345 and .428. With a 3.77 ERA projection from ZiPS, Moylan is an intriguing relief option against right-handed heavy lineups, especially for a team carrying eight relievers who can afford more specialized matchups late in games.


Even if the flaws of any individual reliever concern you, the odds are that one, if not more, of the currently unsigned free agents will enjoy a great 2018. The Cardinals bullpen already projects for the eighth lowest ERA as a collective unit, but that should in no way deter them from rolling the dice on a few sabermetric-savvy moves. Finding cost-efficient production is a crucial competitive advantage both small and large market franchises seek to gain an edge in 21st century baseball.

Why not the Cardinals? What do they have to lose?