Treinen attended Osage City High School in Osage City, Kansas.[1] He played for the school's baseball team as a freshman, but quit during his sophomore year as he developed prediabetes. He returned to the team in his junior year, with his fastball reaching a speed 79 miles per hour (127 km/h).[2]
During Christmas break, Treinen participated in a baseball training camp led by Don Czyz, a retired Minor League Baseball pitcher. Czyz recommended Treinen to Ritchie Price, the head coach of the South Dakota State Jackrabbits baseball team.[2] Treinen transferred to South Dakota State University to continue his college baseball career with the Jackrabbits. He had to sit out 2009 due to the NCAA's rules on transfers. By the time he was able to pitch for the Jackrabbits, his fastball averaged 87 to 88 miles per hour (140–142 km/h). The Miami Marlins selected Treinen in the 23rd round of the 2010 MLB draft. Though Treinen was willing to sign, an MRI revealed shoulder inflammation, and the Marlins withdrew the offer.[2]
In 2011, his senior year, Treinen had a 7–3 win–loss record and a 3.00 earned run average (ERA).[4][5] During the season, his fastball reached 97 miles per hour (156 km/h).[2]
The Nationals invited Treinen to spring training in 2014, where he impressed Nationals' coaches.[3][6][8] He began the season with the Syracuse Chiefs of the Class AAAInternational League, and was promoted to the major leagues on April 12.[9] He earned his first career win on June 29, making a spot start against the Chicago Cubs and out-dueling Jeff Samardzija in a 7–2 win.[10] During the 2014 Washington Nationals season, Treinen appeared both as a starting pitcher and out of the bullpen, with his fastball clocked as high as 98 miles per hour (158 km/h).[11] Splitting the season between the Nationals and the Chiefs, Treinen had a 2.49 ERA in 15 major league games and a 3.35 ERA in 16 minor league games.[12]
For the 2015 season, Treinen started the year in the Nationals bullpen, with the off-season acquisition of Max Scherzer creating a crowded rotation picture. Manager Matt Williams, dealing with injuries to his veteran relievers, began inserting Treinen into high-leverage, late-game situations in early April, occasionally setting up for closer Drew Storen.[13] He also reached 100 miles per hour (160 km/h) with his sinker for the first time in his major league career during the first half of the season.[14]
Treinen remained with the Nationals for much of the year, posting a 3.86 ERA with a 2–5 record with 65 strikeouts for the season. He was optioned back to Syracuse on June 20 after struggling with command for the first half of the season. Upon being recalled the next month, Treinen told The Washington Post that being sent down "was probably the best thing that could have happened" in allowing him to work on his approach.[15] However, even late into the season, Treinen was noted for struggling to retire left-handed batters,[16] ultimately giving up the final run of the Nationals' season on a solo home run by left-hitting New York Mets outfielder Curtis Granderson in a 1–0 loss to the eventual World Series runners-up on October 4.[17]
In the Nationals' 2016 season, Treinen posted a 2.28 ERA on the year and narrowed his platoon splits versus left-handed hitting. He credited veteran teammate Matt Belisle and the Nationals' new pitching coach, Mike Maddux, for helping him improve his craft, while Maddux described Treinen's progress over the course of the season as "puppy dog to bulldog". Treinen led the National League in groundballs induced with 65.9% on the season and ranked highly in inherited runners stranded and soft contact created, among other metrics.[18] Treinen was frequently used in situations when another Nationals pitcher had allowed one or more baserunners and manager Dusty Baker was seeking a double play ball, a role in which he excelled with his high-90s sinker.[19] He remained with the Nationals for the entire year, working exclusively out of the bullpen, and made his first playoff appearance for the team, being credited with the win in Game 2 of the Division Series against the Los Angeles Dodgers and taking the loss in Game 4.[20]
With the departure of Mark Melancon to free agency, the Nationals named Treinen their closer for the 2017 season.[21] On Opening Day, Treinen pitched a perfect inning in the top of the ninth against the Miami Marlins with two strikeouts to end the game, earning the save, the second of his career.[22] The Opening Day performance was the first and last clean inning Treinen pitched in April. He gave up an earned run while notching his second save of the season on April 5 against the Marlins[23] before blowing a save against the same team the following day.[24] After just a couple of weeks as the closer in which he posted a 7.11 ERA, Treinen was removed from the role in favor of Shawn Kelley and later Koda Glover.[25]
In June, Treinen's batting average on balls in play against him gradually regressed toward his career norms.[26][27] But with both Kelley and Glover on the disabled list, fellow setup men Enny Romero and Matt Albers unavailable, and acting manager Chris Speier in need of a reliever to close out the ninth inning of a 4–2 game against the Chicago Cubs on June 29, Treinen was called upon for his first save opportunity since being demoted from the position of closer. He gave up three earned runs for a blown save as the Cubs came back to win 5–4.[28][29]
Second stint with Athletics (2017–2019)
On July 16, 2017, the Nationals traded Treinen back to the Athletics, along with Sheldon Neuse and Jesus Luzardo, for Sean Doolittle and Ryan Madson. At the time of the trade he was 0–2 with a 5.73 ERA and three out of five in save opportunities converted over 37 appearances.[30] As the Athletics' closer, he converted 13 of 16 save opportunities after the trade. In early September, Treinen took three losses in a row, and was on the hook for a fourth, but the A's rallied for two runs in the bottom of the ninth to walk off the Houston Astros 9-8, and Treinen got the win instead.[31] Treinen recorded 13 saves with the A's in 2017, including his last 12 opportunities in a row after blowing three of his first four.
In the first half of the 2018 season, Treinen had a 5–1 record with an 0.79 ERA and 23 saves. He was named an All-Star.[32] He finished the season with a 9-2 record, 38 saves (3rd in the AL), and an 0.78 ERA.[33]
Treinen and the Athletics went into salary arbitration before the 2019 season, and Treinen won, earning a $6.4 million salary for the season.[33]
On June 21, 2019, Treinen was placed on the 10-day injured list with soreness in his right shoulder after an appearance against the Tampa Bay Rays in which he gave up three runs without recording an out. He was activated on July 3, after which he ceded the role of closer to Liam Hendriks.
In 2019 he was 6-5 in 57 relief appearances with 16 saves and a 4.91 ERA, as he struck out 59 batters in 58.2 innings.[34] On December 2, Treinen was non-tendered by Oakland and became a free agent.[35]
Los Angeles Dodgers (2020–present)
On December 15, 2019, Treinen signed a one-year, $10 million contract with the Los Angeles Dodgers.[36] The start of the 2020 season was delayed to late July by the COVID-19 pandemic, but Treinen appeared in 27 games for the Dodgers (3rd in the NL), with a 3–3 record with one save and a 3.86 ERA.[37] In the postseason, he pitched one inning in the Wild Card series, 2+1⁄3 innings in the 2020 NLDS, 5+1⁄3 innings in the 2020 NLCS and 2+2⁄3 innings in the 2020 World Series, allowing six total runs and picking up a save in Game 5 of the World Series. The Dodgers won the championship in six games[37] After the season, the Dodgers re-signed Treinen to a two-year, $17.5 million contract, which also included a team option for a third year.[38]
Treinen pitched in 72 games for the Dodgers in 2021, with a 1.99 ERA, a 6–5 record, seven saves, 85 strikeouts and an MLB-leading 32 holds.[37] In the playoffs, he pitched 1+2⁄3 scoreless innings in the Wild Card Game, allowed one run on one hit with five strikeouts in 3+1⁄3 innings in the 2021 NLDS and one run on three hits in 3+2⁄3 innings in the 2021 NLCS.[37] He came down with a sore shoulder early in the 2022 season which shut him down for the first half of the season.[39] Despite the injury, the Dodgers announced on May 22 that they had signed him to a one-year, $8 million, extension covering the 2023 season and included a conditional option for 2024.[40] He pitched in five games for the Dodgers, allowing one run in five innings[37] while spending most of the season on the injured list, returning from his original injury only to quickly wind up going back on the list.[41]
On November 11, 2022, Treinen underwent right shoulder labrum and rotator cuff repair surgery, with an estimated 10 month recovery.[42] He was expected to return for the start of the 2024 season but suffered a bruised lung in spring training and began the season on the injured list.[43] After a rehab assignment in the minors, Treinen was activated by the Dodgers on May 5.[44] He wound up pitching 46+2⁄3 innings in 50 games, with a 7–3 record, 1.93 ERA and 56 strikeouts.[37]
In 2023, Treinen criticized the Dodgers organization for including the Sisters of Perpetual Indulgence, an LGBT charity, in their annual Pride Night event, saying that it "disenfranchises a large community and promotes hate of Christians and people of faith."[48]