Justin Andrew De Fratus (born October 21, 1987), is an American former professional baseball relief pitcher.

In 2011, De Fratus made his MLB debut and, by 2013, he was a regular member of the Phillies bullpen after a few years of splitting time between the big leagues and Triple-A.

In 2014, De Fratus used his slider to "dominate the league", and establish himself as a reliable reliever, capable of pitching in late-inning situations.

He then attended Rio Mesa High School in Oxnard, California, from which he graduated in 2005;[1] he was a fan of the Los Angeles Dodgers.

[1] He had a successful 2010 season, splitting time between the High-A Clearwater Threshers and Double-A Reading Phillies, and posting a 1.94 ERA with 21 saves in 49 games.

At the end of the season, Baseball America rated him the seventh-best prospect in the Phillies' minor league system.

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.

[13] De Fratus made 61 appearances for Philadelphia during the 2015 campaign, but struggled to a 5.51 ERA with 68 strikeouts across 80 innings of work.

[22] On February 28, 2017, De Fratus signed a minor league contract with the San Diego Padres organization.

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

He again split the season between Tulsa and Oklahoma City, pitching in 25 games (22 starts) and posting a 5.60 ERA and 9–13 record with 98 strikeouts over 141+1⁄3 innings.

[30] After the 2019 season, De Fratus chose to retire from playing to become a minor league coach in the Dodgers system.

[31] On February 23, 2024, De Fratus was announced as a pitching coach for Los Angeles' Triple–A affiliate, the Oklahoma City Dodgers.

[34] 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.

[13] 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.

[35] Especially in the Phillies' young bullpen, the need for reliable late-innings relievers was great, underscoring the importance of De Fratus's emergence.

[14] De Fratus is a devout Roman Catholic who, though he was raised in a large Catholic family, struggled with his faith after an injury early in his career, but ultimately determined the injury was a gift from God to help him better understand his faith: "I really feel that the setback was God telling me, ‘Hey you are not done.

#AllLivesMatter," to which Baer responded with a scathing column on Crashburn Alley, a blog affiliated with ESPN, in which he stated that De Fratus is "complicit in perpetuating a system which inflicts violence on those who didn’t have the luxury of being born white and male and straight and in an economically-stable area.