산 디에고 로얄 SC

On June 20, 2019, San Diego was awarded an expansion team in the USL Championship to debut in 2020 or 2021. Warren Smith, one of the co-founders of Sacramento Republic, was named the President of the new club. Former USMNT, LA Galaxy and San Jose Earthquakes player Landon Donovan was named the Executive Vice President of Soccer Operations. He was named as the club's first manager on November 14. The team's name and crest were developed through fan engagement to reflect the interests of the city. On March 7, 2020, the team played their first competitive match, a 1–1 draw against Las Vegas Lights at their home stadium, Torero Stadium.

The Loyal forfeited a league match against LA Galaxy II on September 25, 2020, following an alleged use of a racial slur by Omar Ontiveros against Elijah Martin, one of the Loyal's black players. The match had been played to a 1–1 draw and Ontiveros was later suspended for seven matches by the USL Championship. A week later, the team forfeited another match against Phoenix Rising by walking out after halftime following the alleged use of a homophobic slur against Collin Martin, an openly gay player, by Junior Flemmings. As a result of the two forfeits, the Loyal failed to qualify for the USL playoffs.

The team reached the playoffs in the 2021 and 2022 seasons, but never advanced beyond the first round. Donovan was later replaced as head coach by former assistant Nate Miller in December 2022.

On August 24, 2023, owner Andrew Vassilanis released a statement that he would shut down the team, and the USL announced that it would transfer the franchise rights of the Loyal due to an inability to find a "viable near- and long-term stadium solution", with the 2023 season set to be the club's last. The team had searched for a venue to replace Torero Stadium but were unable to find suitable facilities in San Diego County; a plan to relocate to Santa Barbara was also considered. The announcement came three months after Major League Soccer announced a San Diego expansion team that would begin play in 2025 as San Diego FC. The club qualified for the USLC Playoffs and played their final match in the Western Conference Quarterfinals on October 22 at Torero Stadium. Loyal lost 4–3 in extra time to Phoenix Rising, who eventually became the champions of the USLC Playoffs.