The 14-time major champ remains loyal to his alma mater, Stanford, but he's also stuck by his hapless Oakland Raiders.
Lefty still supports his hometown team from the left coast, the San Diego Chargers.
The Texan is a Cowboys/Mavericks/Rangers super fan. Through his friend, Cowboys QB Tony Romo, Spieth has enjoyed getting to know a bunch of the team's players. "Boy, it was a really good time getting to know those guys when I root so passionately for them on Sundays. It was kind of a slap-yourself moment that these guys want to meet me, too. It's an awesome experience."
Mahan is such a big Cowboys fan that he even married one of the team's cheerleaders.
McIlroy is a huge fan of Manchester United -- so much so that he got booed by Liverpool fans when he mentioned the team at his claret jug ceremony after winning the 2014 British Open at Hoylake.
Sure, many tour pros are fans of their alma maters, but how many of them have given locker-room pep talks to their school's football teams? Dufner is also a huge Cleveland Browns fan.
Fowler is another tour pro whose support of his alma mater stands out. Here he is on the field before an Oklahoma State football game, and of course, he often wears Cowboys orange on Sundays.
Day grew up in Australia and turned pro instead of going to college, but living in Ohio, he's found a team to cheer for in the Buckeyes.
Like Tiger Woods, Michelle Wie is all about the Stanford Cardinal. She even carries around a "Nerd Nation" notebook when she plays.
The Vermont native is a huge New England sports fan, in particular of the Patriots and Red Sox. His first public appearance after proposing to girlfriend Jillian Stacey? A trip to Fenway Park, of course.
Creamer's love of the San Francisco 49ers includes wearing personalized game-day gear.
The Spaniard is a huge Real Madrid fan -- even if his fiance isn't.
The England export turned Orlando resident has grown quite fond of the NBA's Magic.
The Northwestern grad and Chicago native adopted the hometown Cubs to root for, and has even led the Wrigley Field crowd in singing "Take Me Out to the Ball Game."
The Seattle native is such a big Seahawks fan that he's been asked to represent all Seahawks fans by raising the 12th man banner before a home game.