It takes incredible talent just to be a fringe major leaguer, and even more talent to be a first-round draft pick and a top 10 prospect, as Lucas Giolito was earlier in this decade. Yet last year, the 6-foot-6 righty was The Worst, at least among the 57 pitchers who threw enough innings (162) to qualify for the ERA title. While good health and the White Sox’s commitment to rebuilding allowed him to take the ball 32 times and throw 173.1 innings, Giolito finished his age-23 season with the highest ERA (6.13) and FIP (5.56), and the lowest strikeout-walk differential (4.5%) and WAR (-0.1), of any qualifier. Ouch.
This year, it’s been an entirely different story, as Giolito has pitched like an ace, posting a 3.20 ERA and 3.30 FIP in 157.1 innings en route to 4.7 WAR, good for fourth in the league. When I set out to adapt my “Most Improved Position Players” methodology to starting pitchers, I strongly suspected that the now-25-year-old righty would come out on top, just as Cody Bellinger did in that exercise. He not only did, he was the runaway winner, scoring points in eight of the nine categories I chose to measure. In three of them, he had the largest improvement of any pitcher, and in four others, he ranked among the majors’ top four.
For those unacquainted with my previous foray, its basis is our handy but somewhat obscure Season Stat Grid, introduced just over a year ago. The grid allows the user to view up to 11 years worth of data in a single category, and to track and rank year-to-year totals and changes based on thresholds of plate appearances and innings. Echoing what I did for the position players, and some of the feedback I received (thankfully no tar or feathers), I chose nine statistical categories where we might look for significant, skill-driven changes. To qualify, pitchers needed to have thrown just 80 innings last year, and 120 this year; for the position players, I used 400 plate appearances last year and 300 this year, but in retrospect realized that some very improved players, such as Christian Vázquez, had slipped through the cracks. With pitchers such as the Yankees’ Domingo Germán (who didn’t even crack my top 20) in mind, time I loosened the pitcher thresholds a bit. For the top 20 pitchers whose changes went in the right direction (lower ERA, FIP, walk and home run rates on the one hand, higher WAR and strikeout, first-pitch strike, groundball, and chase rates on the other), I awarded 20 points for first place, 19 for second, and so on. I went 30 deep on the position players, but found that among the pitchers, often the 25th- or 30th “best” change might be a negligible improvement or even a step in the wrong direction.
As with the position players, I make no claim that this is science, and one can certainly quibble with my selection of stats and methodology. I’m effectively rewarding some areas multiple times (this time around, I did away with double-weighting WAR on top of everything else), and my point system steamrolls any sense of scale; the distance between Giolito’s 2.26-run ERA improvement and Homer Bailey’s 1.23-run improvement still yields 20 points for the former and 19 for the latter, with third-ranked Martín Pérez (1.20-run improvement) getting 18 points. Still, I believe this list scans quite well. Here’s the top 20 with the points they received in each category, followed by a closer look at the top 10:
1. Lucas Gioltio, White Sox
Overhauled pitching mechanics, offseason work on the mental aspect of the game, a sinker that’s been mothballed in favor of more four-seamers, and increased use of his changeup, particularly against lefties — there is no shortage of factors that have contributed to Giolito’s turnaround. He gets ahead of hitters far more often, gets them to chase outside the zone more often, and his strikeout rate has practically doubled, from 16.1% to 32.1% (fifth-best in the majors), that while his walk rate has fallen from 11.6% to 8.3%. Even while becoming a fly ball-oriented pitcher (his groundball-to-fly ball ratio has dipped from 1.19 to 0.87), he’s cut his homer rate from 1.4 per nine to 1.08. It’s adds up to one of the most impressive turnarounds of any pitcher in recent memory.
2. Martín Pérez, Twins
When he wasn’t injured, Perez was a pretty solid member of the Rangers’ rotation from 2013-17, but he fell apart last year, getting lit up for a 6.22 ERA and 5.72 FIP in 85.1 innings. The Rangers declined his $7.5 million option, and he signed a one-year-plus-option $4 million deal with the Twins. On the advice of his agent and with the help of new teammate Jake Odorizzi, he added a cutter, which he’s thrown 31.8% of the time, and the early returns were exceptional; through May 23, he pitched to a 2.95 ERA and 3.80 FIP. As Dan Szymborski detailed, the new pitch has become less effective over time, and with it so has the rest of his game; since May 23, he owns a 5.55 ERA and 5.15 FIP. Still, he’s allowed just five runs in 17 innings over his last three starts, and in the big picture, his home run and strikeout rates are much-improved, though the latter really had nowhere to go but up, as last year’s 13.1% was ahead of only Bartolo Colon among pitchers who threw at least 80 innings.
3. Lance Lynn, Rangers
Pop quiz, hot shots: who leads the AL in pitching WAR? Yes, it’s this 32-year-old righty, with 5.8. Throwing more four-seamers and cutters, and fewer sinkers — all from a new arm slot, with a release point that’s shifted an entire foot towards his arm side — he’s dialed up his average four-seam velocity to a career-high 94.7 mph, and his other pitches have gained giddyup as well. With that reworked arsenal, he’s getting ahead in the count more often and getting more swings and misses; his strikeout rate is up (from 23.0% to 27.4%), his walk rate is down (from 10.9% to 6.7%), and his home run rate is virtually unchanged (0.79 per nine) despite a more fly ball-oriented approach. If not for an AL-high .332 BABIP, he’d probably be a Cy Young contender; as it is, the 0.87 runs per nine gap between his 3.85 ERA and 2.98 FIP is the majors’ second-largest.
4. Homer Bailey, Royals/Athletics
After being sidelined at various points by a bulging cervical disc and surgeries to repair his flexor mass and ulnar collateral ligament, and to remove bone spurs — injuries that turned his six-year, $105 million extension with the Reds into quite a disaster — Bailey is finally healthy. His 134 innings is his highest total since 2014, and while his 5.04 ERA is nothing to write home about, it’s down from last year’s 6.09, and his 4.32 FIP is much better than last year’s 5.55. Driven by exceptional results on his split-fingered fastball (41.2% chase rate, 18.6% swinging strike rate, 60.5% groundball rate, and a .179/.211/.300 line on the 140 PA ending with the pitch), his groundball rate is up, his home run rate is down, his strikeout rate is above 20% for the first time since 2016, and he’s a rotation regular for a team that currently occupies the second AL Wild Card slot. Life is good.
5. Luis Castillo, Reds
Castillo’s arsenal — a sizzling fastball, a very good slider, and an increasingly lethal changeup — has turned him into a special pitcher with the rare ability to generate both high groundball and high strikeout rates. The 26-year-old righty has improved from 45.9% to 54.8% in the former, and from 23.3% to 29.1% in the latter; he’s respectively second and fifth in the NL in those two categories, and keeping the ball on the ground has helped him lower his home run rate from 1.49 per nine to 1.07. All of this has elevated him into the top dozen in the NL in ERA (3.21), FIP (3.69), and WAR (3.5). If he can find a way to trim that gaudy 9.6% walk rate, he’ll be a Cy Young contender down the road.
6. Charlie Morton, Rays
The Astros helped the journeyman Morton become a strong enough pitcher to command $15 million per year from the Rays in free agency, and Tampa Bay is getting its money’s worth from the 35-year-old righty, whose 5.2 WAR ranks third in the league. While his 3.13 ERA is a ringer for last year’s 3.11 mark, he’s improved his strikeout, walk, and home run rates — the last to an AL-low 0.71 per nine — en route to a 0.79 drop in FIP (from 3.59 to an AL-low 2.80). Increased use of a curveball/cut fastball combo has been the driver, helping him get a career-best 34.2% chase rate (his 5.4% gain there is the majors’ highest) and better results against lefties .
7. Matthew Boyd, Tigers
The Tigers are so dreadful that they’re on a 114-loss pace, but Boyd provides a glimmer of hope every time he takes the hill. The 28-year-old lefty’s increased used of his four-seamer and curve at the expense of his sinker and slider has helped him to major gains in chase rate, first-pitch strike rate, groundball rate, and strikeout rate; in the last category, his jump from 22.4% to 31.1% is the majors’ second highest, and it’s happened while cutting his walk rate from 7.2% to 6.3%. While he’s lowered his FIP from 4.45 to 4.14, a 40-point spike in his BABIP (from .258 to .298) has kept his ERA more or less in place.
8. Mike Minor, Rangers
Minor’s first year in the Rangers’ rotation — his first in any rotation since 2014 — was quite solid (4.18 ERA, 4.43 FIP, 2.5 WAR), but the 31-year-old lefty has turned in a career year this time around, making his first All-Star team. Even while scuffling somewhat since the start of July, he has ridden an effective four-pitch mix to top-20 improvements in seven of the nine categories here, tied with Pérez and trailing only Giolito; while he’s no higher than seventh in any of those categories, it all adds up to a season that, in tandem with Lynn’s, has helped keep the Rangers relevant.
9T. Madison Bumgarner, Giants
A fractured metacarpal limited Bumgarner to just 21 starts last year, and he posted career worsts in strikeout rate (19.8%), walk rate (7.8%), and FIP (3.99). He’s been healthy as a horse this year; his 91.8 mph average four-seam fastball velocity is his highest since 2015, and his 169.2 innings ranks third in the league. While his ERA is nearly half a run higher than last year (3.71 vs. 3.26) due in part to a 12-point rise in BABIP, he’s gotten ahead of batters 68.% of the time (fourth among qualifiers), gotten them to chase outside the zone 35.2% of the time (his highest rate since 2014), and his strikeout and walk rates have improved to 24.5% and 5.0%, respectively.
9T. Sonny Gray, Reds
Gray’s escape from New York (where he posted a 4.90 ERA and 4.17 FIP last year) and reunion with college pitching coach Derek Johnson have paid great dividends. Thanks to improvements in both his curve and slider — the latter of which he’s using more as a chase pitch than before, with just 28.2% inside the zone — he’s boosted his strikeout rate from 21.1% to 29.0% (the third-largest increase behind Giolito and Boyd); combine that with his already-high 52.3% groundball rate and he’s in a similar sweet spot to Castillo. He’s shaved nearly two runs off his ERA, the third-largest drop, and he’s already more than doubled last year’s WAR (from 1.6 to 3.5).
Brooklyn-based Jay Jaffe is a senior writer for FanGraphs, the author of The Cooperstown Casebook (Thomas Dunne Books, 2017) and the creator of the JAWS (Jaffe WAR Score) metric for Hall of Fame analysis. He founded the Futility Infielder website (2001), was a columnist for Baseball Prospectus (2005-2012) and a contributing writer for Sports Illustrated (2012-2018). He has been a recurring guest on MLB Network and a member of the BBWAA since 2011. Follow him on Twitter @jay_jaffe.