Washington Nationals Free Agent Profile: LHP David Peterson

The Washington Nationals finished with a top-three offense in the 2026 MLB season, but still finished 77-85 because of their struggles on the mound.

After finishing with the third-highest ERA in MLB, all fingers point toward pitching for the Nationals in the offseason. The Nationals will need to fill out their rotation with just three names penciled into their 2027 Opening Day rotation: Cade Cavalli, Connelly Early and Andrew Alvarez.

Starting pitcher David Peterson is somebody the Nationals could call on to fill out the rotation. The 31-year-old left-hander recently finished a successful stint with the Chicago Cubs in the second half of the 2026 season.

He started the season with the New York Mets before being traded to the Cubs for No. 13 prospect first baseman Cole Mathis. 

Peterson’s 2026 season was truly the tale of two halves. Prior to the trade, he posted a 6.09 ERA and 1.65 WHIP in 16 appearances with the Mets. After the move to Chicago, he posted a 3.70 ERA in 16 appearances and 15 starts with the Cubs and finished with a pitching record of 6-2. 

The Nationals allowed 218 home runs in 2026, the fourth most in MLB. Peterson allowed 15 home runs in 148.1 innings pitched. Alvarez would be the only Nationals pitcher with over 90 innings pitched who allowed fewer. 

Peterson finished 2026 with a 6.4 barrel percentage, which is in the 70th percentile of qualified pitchers, according to Baseball Savant. He also finished with a 39.6 hard-hit percentage and an 88.8 average exit velocity, which hover around league average. 

He had his career year in 2024 when he posted a 2.90 ERA and 1.29 WHIP for the Mets. He reached his first All-Star game in 2025 and held a 2.83 ERA until the end of July, before a poor August and September raised his ERA to 4.22.

Peterson pitched a complete shutout against the Nationals in June and had 10 strikeouts and one earned run in eight innings against the Nationals in August of the 2025 season. 

At 31 years old, Peterson would give the Nationals flexibility as a possible long-term piece. He averages just 92.3 miles per hour on his fastball but has a five-pitch arsenal that gives him multiple ways to attack batters without relying solely on velocity, which can help him remain effective as he gets older. 

He will have to prove himself in his eighth season after an up-and-down year, but he could give the Nationals another option in a rotation that desperately needs pitching. If he can prove the struggles at the end of his Mets campaign are behind him, he could become a valuable piece to the Nationals rotation for years to come.