Justin De Fratus

De Fratus attended Rio Mesa High School in Oxnard, California, from which he graduated in 2005; he was a fan of the Los Angeles Dodgers. His high school coach, David Soliz, asserted that he could pitch in the major leagues for a long time, saying, "He definitely has the stuff to pitch in the majors. Justin has the stuff, but he also has the confidence. The odds were against him being drafted in the 11th round out of Ventura College." De Fratus was the first Rio Mesa player to reach the majors during Soliz's tenure. He went on to attend Ventura College where, like at Rio Mesa, he was a starting pitcher.

De Fratus began the 2011 season with Double-A Reading, and was promoted to Triple-A Lehigh Valley on June 16 after much success in Reading. He recorded seven saves with Lehigh Valley, and was named the Phillies minor league player of the week in late August, before making his MLB debut with the Philadelphia Phillies on September 18, 2011, after joining the team as a September callup. During his debut, an opposing batter fouled a ball off, and De Fratus's brother caught the ball. Ultimately, it was a scoreless debut, and he went on to pitch four more big-league games that season. At the end of the season, Baseball America rated him the seventh-best prospect in the Phillies' minor league system. Before 2012, like in 2011, he was given an opportunity to open the season in the Phillies bullpen, but ended up injuring his shoulder, and missing much of the season. He called the injury a "beat down" both physically and mentally, but he returned and pitched with the big-league club in September. At the conclusion of the season, he was mentally exhausted and used golf to help "divert" his attention from baseball, playing over 50 rounds in the offseason; he credited golf with helping him overcome the mental exhaustion he faced after the season, and entered 2013 in a relaxed frame of mind.

By 2013, De Fratus was a regular member of the bullpen, pitching in 58 games with the big-league club; he performed well enough to be considered likely to open the 2014 season firmly implanted in the Phillies bullpen. He broke spring training 2014 with the major league team, but after four appearances, he was optioned back to the minor leagues to work on commanding his pitches, notwithstanding the Phillies' dearth of other right-handed relieving options. While at Lehigh Valley, he spent a significant amount of time reviewing film from his outings in 2011 and 2012, from which he learned that he had a faster pace when pitching, a more aggressive pitching style, and a lower arm slot. Just under a month later, in late May, he was recalled to the major league team, and had much success (11 consecutive scoreless appearances) as part of a Phillies' bullpen that drastically improved from the beginning of the season, and, statistically, was among the best in the major leagues in early June. De Fratus' drastically improved command helped him halve his career walk rate – he walked just 5.5% of batters he faced in 2014, which contributed to a "breakout" season. Although he was overshadowed by the emergence of fellow relief pitcher Ken Giles, De Fratus established himself as a reliable late-innings reliever for the future.

A fastball and a slider comprise De Fratus's pitching repertoire; his fastball averages about 93 miles per hour (150 km/h), but occasionally touches 95 miles per hour (153 km/h), while his slider is about 10 miles per hour (16 km/h) slower than that. His slider was able to "dominate the league" in 2014, and although he does not total as many strikeouts as some relievers, he has established himself as a dependable piece in the Phillies' bullpen. Early in his career, De Fratus aspired to be a closer, but after realizing that an "all-or-nothing" mentality was not necessarily conducive to success, he sought to relax more and focus on being a quality setup reliever, projecting confidence on the mound. Especially in the Phillies' young bullpen, the need for reliable late-innings relievers was great, underscoring the importance of De Fratus's emergence. He is most successful when he utilizes a lower arm angle, and works quickly on the mound.

A free agent following the 2015 season, De Fratus signed a one-year contract with the Seattle Mariners on December 2. He was released on March 16, 2016, and re-signed to a minor league contract the following day.

On June 11, 2016, De Fratus was traded to the Texas Rangers.

On February 28, 2017, De Fratus signed a minor league deal with the San Diego Padres. He was released a month later.

On April 6, 2017, De Fratus signed with the Southern Maryland Blue Crabs of the Atlantic League of Professional Baseball.

On May 9, 2017, De Fratus signed a minor league deal with the Seattle Mariners. He elected free agency on November 6, 2017.

On February 17, 2018, De Fratus signed a minor league contract with the Los Angeles Dodgers. He was named to the mid-season Texas League All-Star Game as a member of the Tulsa Drillers. Overall he made 11 starts for Tulsa and 12 for the AAA Oklahoma City Dodgers, with a 7–9 record and 4.74 ERA. He became a free agent after the season ended and re-signed with the Dodgers on a minor-league deal on January 26, 2019. He again split the season between Tulsa and Oklahoma City, pitching in 25 games (22 starts) with a 5.60 ERA and a 9–13 record. After the 2019 season, he chose to retire from playing to become a minor league coach in the Dodgers system.