Katie Holmes is a sports fan you don't want to mess with.
The 38-year-old actress appeared on The Tonight Show Starring Jimmy Fallon on Wednesday, when she talked about her love of basketball ... and how she isn't above taking things to the next level.
"I'm a big basketball fan, I come from a big basketball family," she explained. "My dad played at Marquette under Al McGuire, so everyone is, like, very good in my family except for me. But we were just at the NCAA this weekend at MSG and it was incredible. We watched the South Carolina-Florida game, and the Florida-Wisconsin game ... oh my God!"
Holmes said she even prays and does rituals before the games.
"I'm a very intense fan no matter what, because I'm the youngest of five, so I used to go to all my brothers and sisters' games when I was little, so ... I pray, I do rituals," she said. "And my nephew was on a great basketball team this year, and I would listen on the radio and I would have to, you know, run on the treadmill because I would be so, like, 'Oh my God, oh my God! It's two minutes left! Oh my God!' you know?"
She of course dials up the intensity if she's actually at the game.
"And then if I'm there, I'm not above yelling anything I want at that ref," she said unapologetically. "Like, 'You're ugly! You suck! I hate you!' ... just to distract. "You're so mean! Those pants are too tight!' You know, anything. I just want to be a part of it."
Holmes also briefly talked about almost nabbing Sarah Michelle Gellar's now iconic Buffy the Vampire Slayer role when she was still in high school.
"I was a junior in high school, and I went out to L.A. for a pilot season, and I tried out for Buffy the Vampire Slayer and ... the scheduling ... well, it didn't work out," she shared. "I got close and then a year later, they were casting Dawson's Creek, so it was weird... and now it's Buffy's 20th reunion."
"She [Gellar] was amazing in that," she added.
Later, Holmes took part in Fallon's adorable Pup Quiz with Girls star Andrew Rannells, where she got to cuddle with a few super cute puppies.
Clearly, Holmes isn't exaggerating when it comes to her love of basketball. Last week, she made sure her 10-year-old daughter, Suri, got in on the NCAA March Madness fun, when she took her to a Notre Dame basketball game at the Barclays Center in Brooklyn, New York.
Check out Holmes' hilariously intense face watching the game in the video below!