Foster Griffin Could Be a Sleeper Free Agent Reliever for the Royals

Priority number one for Royals GM JJ Picollo has been acquiring a couple of outfielders to boost the lineup in 2026. He made that clear in many interviews during the Winter Meetings in Orlando this week, pointing out that they would hit the free-agent and trade markets this winter to accomplish those goals.

However, that isn't the lone need roster-wise this offseason. According to Anne Rogers of MLB.com, Kansas City is also interested in acquiring a left-handed reliever who can specialize in getting left-handed hitters out.

The Royals currently have three lefties projected to be in the bullpen on Opening Day in 2026, according to Roster Resource: Angel Zerpa, Daniel Lynch IV, and Bailey Falter. That said, based on Rogers' report, it seems like the Royals are looking for a boost in left-handed relief, or they could be on the verge of trading one of those three this offseason to acquire a much-needed bat.

There aren't a ton of left-handed relief options on the free-agent market, according to Spotrac. The highest-profile lefty relievers in terms of market value are Caleb Thielbar ($5.4 million), Brent Suter ($4.4 million), Danny Coulombe ($4.3 million), and Andrew Chafin ($4.2 million). The youngest in the group is Chafin, who is 35. 

Hence, many of the lefties they could acquire on the free-agent market will not just be expensive but may not be worth more than a one-year deal, given their ages. 

One out-of-the-box option could be Foster Griffin, a former Royals draft pick who has spent the last three years in NPB (Nippon Professional Baseball) with the Tokyo Giants. After posting a 1.62 ERA, 0.95 WHIP, and 1.78 FIP in 78 IP with the Giants last season, Griffin announced his intention to return to Major League Baseball in 2026. 

Given his time in Japan, it isn't easy to gauge his value or the interest of other teams this offseason. However, Griffin could be the lefty that the Royals desire this offseason, and he could also hold some long-term value as well, as he is just 30 years old. 

Let's dive into Griffin's background, both in the States and Japan, and what he could bring to the Royals' pitching staff next season.

Former Royals First Round Pick Struggled With Injury and Generating Strikeouts

Griffin has a long history with the Royals, as he was drafted 28th overall in the 2014 MLB Draft.

The tall, projectable lefty, drafted out of The First Academy in Florida, had a rocky start in the Royals' system. Initially, Griffin struggled to strike batters out at each level in the Royals' farm system. From 2014 to 2017, across Rookie to Double-A ball, he posted a K rate over 20% just once (26.1% in High-A in 2017).

As a result, his ERA numbers fluctuated over those four years.

In 2014, he posted a 3.21 ERA in 28 IP in Rookie ball. In 2015, he had a 5.44 ERA in 102.2 IP in Low-A ball. In 2016, he had a 5.43 ERA in 132.2 IP across Low-A and High-A ball. And in 2017, his best season in the Minor Leagues at that point in his career, he put up a 3.35 ERA in 161.1 IP across the High-A and Double-A levels. His strong performance earned him a spot in the Futures game that season in Miami.

When the strikeouts have been up, better results have tended to follow for Griffin in the Minor Leagues. 

In 2020, during the COVID pandemic, Griffin made his MLB debut. However, he suffered an elbow injury in his first career appearance (1.2 IP), and he underwent Tommy John surgery shortly after. The lefty was able to return in 2021, posting a 3.81 ERA, 23.1% K rate, and 1.29 WHIP in 52 IP in the Minor Leagues that season (which spanned from the Low-A to Triple-A levels).  

Griffin was able to make his way back to the Royals in 2022 after posting a 1.93 ERA and 29.4% K rate in Triple-A Omaha. However, his return to the big leagues was difficult, as he posted a 12.46 ERA, 5.65 FIP, and -8.3 K-BB%. As a result, the Royals designated him for assignment, and he was traded to the Blue Jays for right-handed pitcher Jonatan Bernal. 

Griffin primarily pitched in Triple-A Buffalo for the Blue Jays organization, posting a 2.31 ERA, 24.8% K rate, and 3.21 FIP in 23 IP. Unfortunately, that wasn't enough for him to earn much of a chance in Toronto, as he only made one appearance with the Blue Jays. When looking at his metrics via TJ Stats, Griffin leaned heavily on his cutter at the Major League level with mixed results.

Between 6.1 IP with the Royals and Blue Jays, Griffin posted a 97 TJ Stuff+ overall. His cutter rated as his best pitch overall with a 102 TJ Stuff+, 56 grade, and 71.4% zone rate. While he did flood the zone well (54.1% overall zone rate), he struggled to generate chase (15.7%), whiff (25%), and gave up a lot of hard contact (.453 xwOBACON).

As a result of these mediocre metrics, the Blue Jays released him at the conclusion of the 2022 season, and he signed with the Yomiuri Giants of the NPB (based in Tokyo). 

Turning Things Around in Tokyo With the Yomiuri Giants

The move to Japan was a revelation for Griffin, who became a bona fide ace in his three seasons with the Giants.

In 54 appearances and 315.2 IP with the Giants, he posted a 2.50 ERA, 1.05 WHIP, and a 4.55 K/BB ratio. He showcased excellent command with Yomiuri and limited the long ball in his tenure in the NPB. He posted HR/FB rates of 8.6% and 9.3% in 2023 and 2024 before posting a NPB career-low rate of 1.6%. Griffin also did an excellent job of not just limiting home runs but also inducing strong groundball rates with the Giants. That is evidenced by his 53.3%, 47.8%, and 48.9% groundball rates in 2023, 2024, and 2025, respectively.

The strikeouts also improved and remained stable in his three-year tenure in Japan. From 2023 to 2025, he posted strikeout rates of 23.3%, 26.9%, and 25.1%, respectively. Considering the troubles some USA-born pitchers have had in their transition to the NPB (cough...Trevor Bauer...cough), Griffin's excellent performance in his three seasons with the Giants should be lauded. 

Griffin looked easy and dominant at times on the mound, as illustrated in this nine-strikeout performance he had last season against the Seibu Lions. 

In three seasons with the Yomiuri Giants, Griffin looked every bit like the ace the Royals were hoping he would develop into when they drafted him in the first round in the 2014 MLB Draft. 

What Could He Bring to the Pitching Staff in Kansas City?

Obviously, the results were much better for Griffin in Tokyo than in the Minor Leagues here in the States. However, what was the difference for Griffin over the past three seasons? 

A lot could be credited to his change in pitch mix. That included the addition of a splitter and slider to his arsenal, as well as heavier usage of the four-seamer and less usage of the cutter. 

Below is a look at his pitch arsenal last year with the Giants, along with metrics for each pitch, including usage, velocity, strike rate, whiff rate, and batting average against. 

As Royals fans can see above, Griffin's most-thrown pitches were his four-seamer (39.2% usage), slider (18.2%), cutter (16.2%), and changeup (10.6%). He threw the knuckle curve (5.8%), splitter (5.7%), and two-seamer (4.3%) more sparingly. However, his seven-pitch mix last year was much more robust than his four-pitch repertoire back in 2022. 

His changeup, splitter, and slider were his best offerings in terms of whiff rate, as they generated rates of 50%, 42.9%, and 37.8%, respectively. While the four-seamer didn't create a ton of whiff (13.8%), he threw strikes with it (48.1% strike rate) and limited productive contact (.232 batting average against). 

Even though Griffin averaged only 90.2 MPH on the four-seamer, he was able to attack hitters with the offering on the edges, especially left-handed ones, as illustrated in the clip below. 

The four-seamer was not a great swing-and-miss offering. Still, it set up his other offerings well, especially his changeup and slider, his primary offspeed and breaking offerings, respectively. 

His changeup was his best swing-and-miss pitch, as it sported a 50% whiff rate. The pitch had similar movement to his four-seamer but considerable vertical drop and a sizable velocity difference (8.6 MPH, specifically). Those factors helped produce nasty whiffs like this one below. 

When it came to his slider, the breaking offering averaged 80.3 MPH, an even greater velocity drop from the four-seamer (9.9 MPH difference). That helped him induce a whiff rate of 37.8% on the pitch. Griffin's slider was not a loopy one but a late-breaking one, which contributed heavily to his success with it during his tenure with the Giants. 

The pitch was a nasty offering, especially for left-handed hitters, as seen in the clip below against the Lions.

Griffin presents a unique weapon for Kansas City, should JJ Picollo opt to sign him this offseason.

As seen in the clips below and in his overall numbers, the 30-year-old lefty can be an effective middle-innings reliever who can shut down left-handed batters in key spots, at the very least. His seven-pitch arsenal is diverse enough to be effective over 1-3 innings stretches, which is what the Royals need over the course of a full 162-game season.

Furthermore, there could be some spot starter upside with Griffin as well, should they decide to commit to him with a multi-year deal. 

Griffin could bring that flexibility to the Royals' pitching staff, as Michael Lorenzen did a year ago, seamlessly jumping between the bullpen and rotation. The Giants rode him heavily as a starter over the past three years in the NPB, but his mix and stuff are good enough to handle shorter stints (and may play up more in those spots as well). That said, should injury hit the Royals' rotation, Griffin could handle a starting stint better than other lefties like Lynch or Falter, who have been starters in the past. 

Griffin may not have the MLB pedigree of other free-agent relievers currently available. That said, Griffin's combination of intriguing pitch arsenal, relative youth, and versatility should make him a target for Picollo and the Royals. He could stabilize the bullpen not just for next year, but beyond as well.