The play didn't have an impact on the outcome of the Royals' wild 7-6 win at Boston on Tuesday, but this was one of the rarest plays you'll see in a game.
The Royals had runners on first and second with two outs and Lucas Duda at the plate. Boston catcher Christian Vazquez blocked a pitch from Carson Smith, and the ball was on the ground next to him. Vazquez used his catcher's mask to secure the ball, and that's not allowed.
Home plate umpire Chris Conroy was watching Vazquez and immediately made his ruling. Jon Jay and Ryan Goins were allowed to advance one base because of Vazquez's miscue, which was ruled an error.
Major League Baseball Rule 5.06 is about running the bases, and Vazquez's no-no is actually in Rule 5.06(b)(3)(E), which says: "A fielder deliberately touches a pitched ball with his cap, mask or any part of his uniform detached from its proper place on his person. The ball is in play, and the award is made from the position of the runner at the time the ball was touched."
That is what happened here as you can see in this video from Chris Lilly of WIBW:
There was some chatter that the play was a catcher's balk, but this was simply an error.
However, there is a rule on a catcher's balk.
Rule 5.02(a) says a catcher's balk happens when the catcher is out of position on a pitch: "Except that when the batter is being given an intentional base on balls, the catcher must stand with both feet within the lines of the catcher’s box until the ball leaves the pitcher’s hand."
Vazquez's play was a rarity, but I found a couple of instances of it happening.
In 2010, Mariners catcher Adam Moore was caught using his mask to get a ball. In 1995, the Dodgers beat the Pirates when Pittsburgh's Angelo Encarnacion stopped a ball with his mask and the game-winning run trotted home in the 11th inning.
At that time, it was a two-base error, and had that been the case this season, the Royals would have scored on Vazquez's error. But that would have taken away from the dramatic 12th inning.