Chicago Cubs ace Jon Lester all but confirmed rumors Monday that he has a case of the “yips” when it comes to throwing the ball to first base. The 31-year-old lefthander botched not one, but two pickoff attempts against the Cincinnati Reds, just as gossip about his apparent malady reached an all-time high.

Lester’s first pickoff attempt of the game pulled first baseman Anthony Rizzo far off the bag, Deadspin notes. His second pickoff throw sailed over Rizzo’s head into right field, where Cubs outfielder Jorge Soler scooped up the ball and threw out the runner who tried to advance to third. Chicago ultimately won the game, 7-6, and Lester downplayed his throwing misses after the game.

“When you’re not used to doing stuff like that, I got a little overexcited and threw the ball too soon,” Lester said, according to the Chicago Tribune. “Once again, [Soler] picks me up.”

But there’s evidence that Lester’s errant throws were due to more than just poor timing. Before Monday’s game against the Reds, he hadn’t attempted a pickoff throw to first since April 30, 2013, according to ESPN. A source from the Red Sox, Lester’s former team, told the Boston Globe this week the franchise was well aware of Lester’s yips and tried to help him overcome them, while a scout from an American League team said he included data on Lester’s problems in his reports.

“Part of how the Red Sox kept Jon Lester’s throwing issue under wraps was by having him do his work on back fields in spring training,” ESPN reporter Buster Olney tweeted Monday night.

The Cubs tried this week to downplay the notion that Lester had the yips, a mental block that prevents physical action. When asked before Monday’s game if the rumors were overblown, Cubs manager Joe Maddon responded with a simple “Yes.” And Lester said on April 8 that his throwing to bases “wasn’t a big issue until someone brought it up on TV.”

But teams have begun to take notice. The St. Louis Cardinals stole three bases against Lester on Opening Day, and the Reds swiped another bag against him on Monday. Lester allowed 16 steals throughout all of last season.

The yips aren’t a new phenomenon in baseball, or in sports in general. Former New York Yankee Chuck Knoblauch and former Los Angeles Dodger Steve Sax, both second basemen, each lost the ability to make routine throws to first base. Former St. Louis Cardinals outfielder Rick Ankiel began his career as one of the sport’s most promising pitchers, but completely lost control over his pitches during the 2000 National League playoffs and never recovered it.

The yips are also common in golf. Many observers suspected “chipping yips” were responsible for the collapse of Tiger Woods’ short game earlier this year, when on-course struggles forced him to take a two-month hiatus from the sport. For any athlete, the yips typically result during a crisis of confidence. Lester attempted 247 pickoffs from 2009 to 2011, according to Fangraphs. He tried just 12 from 2012 to 2014.

“It’s a mental roadblock that causes a physical problem,” said Grayson Zacker, director of instruction at the Jim McLean Golf School at the Trump National Doral in Miami.