Gruden had changed into a Las Vegas Raiders cap by the second quarter.
"I apologize for not having the right hat on. Somebody played a pretty good trick on me," Gruden said after the Raiders fell to the Chargers 30-27 in overtime.
The Raiders are in their first season in Southern Nevada after calling Oakland, California, home from 1995 through 2019. They were in Los Angeles from 1982 to 1994 and Oakland before that from their inception in the AFL in 1960.
Jon Gruden still "adjusting" to the Raiders' new home city 😅 pic.twitter.com/gCyHGD16iI— NFL on ESPN (@ESPNNFL) December 18, 2020
Gruden is in his second tenure with the franchise, having coached the Raiders from 1998 to 2001 and again since 2018, and has long called himself a fan of the team.
The Raiders, who began their season 6-3, have now lost four of their past five games and lost quarterback Derek Carr to a groin injury against the Chargers. He was replaced by Marcus Mariota as Las Vegas dropped to 7-7 on the season and most likely out of the playoff picture.