I know it’s soccer, BUT….
the U.S. Women's National Team (USWNT) lost a scrimmage to the FC Dallas U-15 boys academy team in 2017, with the score being 5-2. The match was part of their preparation for friendly matches against Russia. While it was a scrimmage and not a formal game, the result was notable, especially considering the USWNT's reputation as one of the top teams in the world.