Colorado Rockies (2016–2017) The
Colorado Rockies of
Major League Baseball (MLB), Hammer's hometown team, selected him in the 24th round, 710th overall, of the
2016 MLB draft. He signed with the team for a
bonus of only $1,000 and was assigned to the
Rookie-level Grand Junction Rockies of the
Pioneer League. The Grand Junction Rockies were managed at the time by Frank Gonzales, who had coached Hammer when he was in high school. Hammer made 27 Pioneer League appearances, all in relief, in his first season of professional baseball. He posted a 0–2 record and a 3.92 ERA while striking out 52 batters in innings. Hammer opened the 2017 baseball season as the designated
closer for the
Single–A Asheville Tourists. After going 3–1 with a 1.08 ERA, 40 strikeouts, and six saves in his first 25 innings, he became one of six Tourists named to the
South Atlantic League Mid-Season All-Star Team that June. He pitched five more innings, earning another win and striking out two more batters, before being called up to the
High–A Lancaster JetHawks. In 12 games there, Hammer went 0–1 with a 5.25 ERA, striking out 18 batters in 12 innings and converting six saves.
Philadelphia Phillies (2017–2021) On July 26, 2017, the
Philadelphia Phillies traded sidearm reliever
Pat Neshek and cash to the Rockies in exchange for three
prospects: Hammer, Alejandro Requena, and Jose Gomez. Hammer was assigned to the High–A
Clearwater Threshers of the
Florida State League (FSL), becoming a
bullpen staple with a 2–0 record and a 0.57 ERA in 12 appearances. Hammer struck out 20 batters in FSL innings, issued only two
walks, and held his opponents to a .154
batting average. Impressed with his regular season performance, the Phillies sent Hammer to the
Arizona Fall League to continue working on his pitch mechanics as a member of the
Glendale Desert Dogs. In 10 appearances for Arizona, Hammer posted an ERA of 0.66, with 11 strikeouts in innings and only 0.805
walks plus hits per innings pitched (WHIP). He appeared in only three games, allowing three
earned runs in innings before going on the
disabled list (DL). He spent most of the season on the DL with a strained elbow, appearing in only 12 games. Nine of those appearances were in relief for the Threshers, with whom he went 1–2 with a 2.79 ERA and struck out 12 batters in innings. The other three were quick outings with the
Gulf Coast League Phillies. He made one appearance for the
Triple-A Lehigh Valley IronPigs as well, recording
outs against all six batters he faced. He made his MLB debut the following day, pitching a scoreless inning against the
Milwaukee Brewers by getting out
Christian Yelich,
Ryan Braun, and
Mike Moustakas. Hammer played 20 games with the Phillies, during which he went 1–0 with a 3.79 ERA and 1.421 WHIP while striking out 13 batters in 19 innings. He was sent back down to the IronPigs on July 23, however, to prevent him from being overworked following his injury-shortened 2018 season. Upon his return, Hammer's
fastball velocity sharply declined with the rigors of a full season of professional baseball, and in his last 16 outings, he recorded a 14.49 ERA, .345
batting average against, and opposing batters had a 1.128
on-base plus slugging against him. Coupled with his earlier appearance, Hammer went 2–2 with a 12.64 ERA in 17 games for Lehigh Valley, striking out 16 batters in innings. but on June 30,
Minor League Baseball responded to the
COVID-19 pandemic by cancelling the season. Every team was afforded a 60-player pool, of which 30 were on the major league roster and the other 30 practiced an at alternate training site instead of playing in minor league games. Hammer was included in the alternate training site player pool, and he spent the entirety of the abbreviated season training in Lehigh Valley. Hammer opened the 2021 season with the IronPigs, posting a 1.74 ERA and striking out 33 batters in innings before he was called up to Philadelphia on July 10. He made his season debut that day against the
Boston Red Sox, loading the bases on a
hit by pitch, a
single and a
walk before retiring the next three batters to escape the inning without allowing a run. Hammer appeared in 20 major league games during the 2021 season, recording a 4.95 ERA and striking out 22 batters in 20 innings. On November 5, 2021, the Phillies attempted to
outright Hammer off of the 40-man roster, but he opted for
free agency instead.
Second stint with Rockies (2022) On December 1, 2021, Hammer signed a minor league contract with the Rockies to rejoin the team that drafted him. Following the
2021–22 MLB lockout, Hammer was one of ten non-roster players that the Rockies invited to a condensed spring training. He was assigned to the
Albuquerque Isotopes, the Triple-A affiliate of the Rockies, to begin the season. The assignment reunited Hammer with his high school baseball coach Frank Gonzales, who had since taken a job as pitching coach for the Isotopes. He spent the entire season in Albuquerque. In 53 appearances for the Isotopes, all of which came in relief, Hammer was 1–1 with a 5.94 ERA. He struck out 47 batters in 47 innings. He made his Frontier League debut in the Crushers' season opener, pitching a scoreless inning in relief against the
Québec Capitales on May 12. The Crushers also deployed Hammer as a starting pitcher, and he picked up his first win on June 21, pitching five innings in a shutout of the
Schaumburg Boomers. In 19 appearances for Lake Erie, including nine starts, Hammer was 3–3 with a 3.46 ERA, striking out 46 batters in 52 innings.
Los Angeles Angels (2023) On July 29, 2023, Hammer signed with the
Los Angeles Angels organization, He made his debut with the Triple-A
Salt Lake Bees on August 3 as a starter, allowing one run in five innings against the
El Paso Chihuahuas. He made nine appearances with the Bees, all but one as a starter. During that Time, Hammer went 1–2 with a 6.63 ERA, striking out 19 batters in 38 innings. Two months later, the Mexican League would suspend the Generales for the 2024 season. Hammer was officially released by the
Caliente de Durango without appearing in a game on September 21. == Pitching style ==