The One Direction star, 20, donned Sam's Rams jersey during a concert in St. Louis this week. As GLAAD officials pointed out, the move coincided with Sam surviving the first round of NFL roster cuts.
The St. Louis Rams tweeted a photograph of Styles rocking the Sam jersey during his band's Aug. 27 performance.
Meanwhile, Sam took to Twitter to thank the pop star for his support.
Earlier this week, ESPN sparked national controversy after reporting on Sam's showering habits during the St. Louis Rams training camp. The network later apologized, saying the segment "failed to meet the standards we have set in reporting on LGBT-related topics in sports."