Adams began the 2017 season with the Class- AAA Syracuse Chiefs of the International League. With the Nationals' bullpen struggling over the first half of the 2017 season, Adams was mentioned by The Washington Post in a July 12 article among several minor league pitchers the team could consider calling upon as reinforcements. Two days later, Adams was called up to the big leagues for the first time, along with Syracuse teammate Trevor Gott, after the Nationals optioned struggling left-handed reliever Sammy Solis and assigned ailing starter Joe Ross to the disabled list with an elbow sprain. Adams made his major league debut on July 15, 2017, against the Cincinnati Reds, loading the bases on an error, a walk, and a wild pitch and then walking in a run and allowing a single before he was pulled from the game. Adams was optioned back to Syracuse on July 18, his earned run average still standing at infinity due to the earned run he allowed without recording an out. Adams was recalled by the Nationals on September 1, 2017, and recorded his first major league outs in an inning of relief against the Milwaukee Brewers on September 3, after loading the bases.
2018
Adams began 2018 with Class AAA Syracuse. On April 22, the Nationals called him up to the major leagues. He pitched on April 25 in a 15-2 Washington win over the San Francisco Giants at AT&T Park in San Francisco, giving up a hit and a walk but no runs in one inning of work. On April 28, Nationals manager Dave Martinez brought him in to relieve left-hander Sammy Solis in the 10th inning of a game at Nationals Park in Washington, D.C., against the Arizona Diamondbacks with one out, runners on second and third, and the score tied 3–3. Martinez intended Adams to face right-handed utility player Chris Owings, who was waiting in the on-deck circle. However, Martinez made the mistake of making the pitching change before the public address announcer had announced Owings as the batter. With Adams in the game, Diamondbacks manager Torey Lovullo took advantage of Martinez′s error by recalling Owings and sending left-handed outfielder Jarrod Dyson to the plate, forcing Adams to face a left-hander rather than a right-hander as Martinez had intended. Adams walked Dyson to load the bases. With only one reliever – Carlos Torres – remaining in the Washington bullpen, Martinez left Adams in to face the next batter, center fielder A. J. Pollock, as well, and Adams also walked Pollock, forcing in what turned out to be the winning run in a 4–3 Diamondbacks victory. On April 29, the Nationals optioned Adams back to Syracuse. Adams was designated for assignment on April 30, 2019, following the selecting of Dan Jennings’ contract.
Seattle Mariners
On May 4, 2019, the Nationals traded Adams to the Seattle Mariners for left-handed minor-league pitcher Nick Wells and cash considerations. He was assigned to the Tacoma Rainiers. On May 13, he was called up to the major league roster. He registered an ERA of 3.77 in 29 games.
Pitching style
In 2014, a report on Scout.com took note of Adams' "loud, earth-shattering slider", describing it as a pitch "like hardly any other". Adams also throws a fastball in the 92-94 mph range. Despite an effective two-pitch mix, Adams has been noted for problems with his command, walking more than seven batters per nine innings in the first half of the 2017 season with the Class-AAA Syracuse Chiefs.
