Sister Mary Jo Sobiek bounced the ball off her bicep as she prepped for the honor.
Then she threw a perfect strike from the mound, to the delight of the crowd.
Sister Mary Jo is with Marian Catholic High School, which was honored at the stadium as the White Sox took on the Kansas City Royals.
Sox pitcher Lucas Giolito was impressed.
One of the most impressive first pitches of all time. 😱 pic.twitter.com/PA7M4iC9X5— Chicago White Sox (@whitesox) August 18, 2018
"That was awesome," Giolito said after the game. "She had a whole routine. She had it planned out. I was just lucky to be back there. She threw a perfect pitch."
"She was pretty good, actually," White Sox manager Rick Renteria said. "We talked to her a little bit but before we were talking to her, she was talking to someone and she wanted to warm up. She had a mitt and a ball. She gave him the mitt. She stepped back at about 45 feet and threw a bullet."
Unfortunately, the perfect first pitch didn't bring luck to the home team, which fell to the Royals 3-1.