Nix grew up playing youth baseball as a catcher. He was involved in a home plate collision at the age of 11 that led to chronic pain in his back, and required spinal fusion surgery, which he had at the age of 12. He grew up a Cardinals fan. Nix attended Los Alamitos High School in Los Alamitos, California, and played for their baseball team. He played as a catcher until his freshman year, when he was needed as a pitcher. In his junior year, Nix pitched to a 7–2 win–loss record with a 2.80 earned run average, and was named to the Press-Telegrams all-area first team. He committed to attend the University of California, Los Angeles on a college baseball scholarship to play for the UCLA Bruins baseball team. At the start of his senior year of high school, Nix played for the United States national baseball team in the 2013 18U Baseball World Cup. The United States won the gold medal in the event. By the start of his senior season, his fastball velocity ranged from. The Houston Astros selected Nix in the fifth round, with the 136th overall selection, of the 2014 Major League Baseball draft. Nix and the Astros agreed to terms on a contract, including a $1.5 million signing bonus, well above the $370,500 recommended at the 136th slot. However, the Astros failed to come to terms with Brady Aiken, the first overall selection of the draft, which reduced their allotted draft pool, leaving them unable to sign Nix without incurring penalties. The Astros reneged on their agreements with Nix and Mac Marshall, and offered Nix a $616,165 signing bonus, which was the most the Astros could offer him without incurring penalties. Nix rejected the offer. He filed a grievance against the Astros, which put his collegiate eligibility in jeopardy. The two sides reached a settlement in December, but did not disclose the terms. Rather than wait for a ruling on his collegiate eligibility, Nix opted to take a post-graduate year at the IMG Academy in Bradenton, Florida, to play for their baseball team. In this way, he became eligible for the 2015 MLB draft. After watching him throw for scouts, Keith Law, a draft expert for ESPN, wrote that he believes Nix could be a first-round pick. In ten starts for the IMG Academy, Nix improved his fastball velocity to, improved his changeup, and developed a curveball.
Professional career
Nix did not consent to being reselected by the Astros in the 2015 draft. The San Diego Padres selected Nix in the third round, with the 86th overall selection, of the draft. He signed with the Padres, receiving a $900,000 signing bonus. Nix was assigned to the AZL Padres, where he spent the whole season, pitching to a 0–2 record with a 5.49 ERA in seven games. In 2016, Nix pitched for the Fort Wayne TinCaps of the Class AMidwest League, where he posted a 3–7 record with a 3.93 ERA. Nix spent the 2017 season with both the Lake Elsinore Storm of the Class A-AdvancedCalifornia League and the San Antonio Missions of the Class AATexas League, where he went a combined 5–5 with a 4.67 ERA between both teams. In 2018, the Padres invited Nix to spring training. Nix made nine starts for San Antonio, pitching to a 2.05 ERA, and then made one start for the El Paso Chihuahuas of the Class AAAPacific Coast League, not allowing a run, before the Padres decided to promote Nix to the major leagues to make his debut on August 10. He made nine starts, going 2–5 in innings and a 7.02 ERA. Nix suffered a tear in his ulnar collateral ligament of the elbow in March 2019. He elected to rehab the injury and forgo surgery. Nix returned to game action on July 26, and made rehab appearances for the AZL Padres, Lake Elsinore, the Amarillo Sod Poodles, and El Paso. Following the 2019 season, Nix made one appearance for the Peoria Javelinas of the Arizona Fall League. Nix was designated for assignment on November 4, and outrighted to El Paso on November 11.
Legal issues
On October 6, 2019, Nix was arrested and charged with criminal trespassing, having allegedly broken into a house in Peoria, Arizona, through a doggy door. An inebriated Nix was kicked in the face and tased by the homeowner prior to Nix fleeing, and was arrested by local police not far from the scene.
