They are called the yips. And for those boys of summer within baseball and golf who are afflicted, they can make the season long and stressful.

Yips are the sudden and often unexplained disruptions to motor skills in athletes. They can be very disruptive — even career-ending for some requiring intervention from coaches, therapists and trainers. For years, the yips were considered to be the result of stress, but there is now consideration being given to many cases of the yips having a physical basis known as a focal dystonia.

The origination of the term "yips" is attributed to Tommy Armour, a notable golfer from Scotland. After a long successful sports career in the 1920s, Armour began having problems with his putts.

The disruption to performance for athletes has gained the most attention among golfers and professional baseball players. Notable athletes who have suffered from the yips include:

  • Steve Sax (baseball, second base)
  • Chuck Knoblauch (baseball, second base)
  • Steve Blass (baseball, pitcher)
  • Rick Ankiel (baseball, pitcher)
  • Mackey Sasser (baseball, catcher)
  • John Starks (basketball)
  • Nick Anderson (basketball)
  • Chuck Hayes (basketball)
  • Mike Vanderjagt (football, kicker)
  • Nick Folk (football, kicker)
  • Braylon Edwards (football, wide receiver)
  • David Duval (golf)
  • Sergio Garcia (golf)
  • Ben Hogan (golf)

Yips can appear in a variety of forms. Some athletes may experience muscle twitches and jerks. For others, no unusual motor phenomena may be involved, just timing imperfections. They most frequently occur among athletes who perform intricate, precise actions. This includes pitching/throwing, shooting free throws, golf putting and kicking.

In baseball, a specific version of the yips may be referred to as "Steve Sax Syndrome" — a sudden inability to throw to first base or "Blass Syndrome" newly reduced skills in the outfield.

"It's amazing when you talk to people, it doesn't matter when they played or where they played, all the symptoms are exactly the same," Sax had reported to Fangraphs this season. "Something triggered it. They hit somebody. They threw a ball away to end a game. 'I hit somebody when I was pitching in batting practice.' Something triggers it. It's a horrible thing. I started thinking about it. Basically, I just lost my confidence. Over the course of the season, I started a campaign of negative thinking."

But it may not be simply a mental issue.

Kyle Bradford Jones, M.D., of the Department of Family and Preventive Medicine, University of Utah, and two colleagues recently published a case report in the Journal of Family Practice about the experiences of an athlete. They concluded that what was originally considered to be the yips was a problem that was physical in origin.

"Athletes who play sports that require precision movements commonly develop the yips," they concluded. "While the prevailing theory among athletes is that this is a psychological phenomenon, evidence shows that this may in fact be a neurologic focal dystonia caused by repetitive use. Greater awareness of yips as a possible organic, treatable neurologic condition is needed in order to stimulate more research on this topic."

Yips may also result in a fear of becoming reinjured after a sidelining event. When there are injuries or changes in physical performance among athletes, both the physical and psychological impact needs to be taken into account.

"It's important to have team doctors understanding illness and injury, regardless of medical recovery. I think these are important factors. Oftentimes these are the things that make a difference in the athlete," David Coppel, Ph.D., a neuropsychologist from the University of Washington and an authority on sports medicine, said in an interview with MedPage.

Yips can impact careers and challenge the loyalty of fans. Each season may bring the yips to yet another athlete, and it is certainly a challenge to those athletes afflicted.