From "Back strain, 'yips' land Kuo on DL" by Gurnick at Dodgers.com:
In May 2009, the Dodgers put reliever Hong-Chih Kuo on the disabled list with what was called a "left elbow strain." And his elbow was strained, but it turned out he also had a case of the "yips," a loss of certain motor skills often used by golfers to explain shaky putting, but adapted in baseball for players who suddenly can't control throws with no loss in velocity.
On Saturday, the Dodgers put Kuo on the disabled list with what was called a "lower left back strain," and his back does have an issue, but apparently he also has a relapse of the yips.
During pitchers' fielding practice on Friday, two of Kuo's throws to second base sailed and bounced into center field. He tried to warm up in the bullpen during the eighth inning of a blowout loss and wasn't able to throw a strike, prompting the decision to recall right-hander Ramon Troncoso and put Kuo back on the disabled list.
Two years ago, Kuo attempted a similar bullpen session and airmailed two pitches onto the field that stopped play. This time he wasn't as wild, but he was wild enough.
Bill Shaikin of the LA Times offers a similar story, but eschewing the term "yips." Kuo's status is an effective reminder of the significance of the mental game of baseball — especially as we watch Jonathan Broxton's varying performances, or marvel at the rejuvenated Matt Kemp. You can't turn off your brain!