The rules are that both the batter and the pitcher can switch sides once per at-bat. The umpire in this case made the ruling that the batter had to declare his intention first. While the rule that both can switch sides once is correct, and in the rulebook, the decision that the batter must declare first was an interpretation, and the NY-Penn League is trying to get an official ruling from Major League Baseball on how that situation should be handled.
Originally posted by the Lohud Yankees blog"The only rule is what when a pitcher is on the rubber, a batter cannot change boxes,” [MLB Crew Chief Charlie] Reliford said. “But there is no penalty for switching, you just tell him he can’t do it.”
The MLB Rules Committee (which meets infequently) will have to address the situation and decide what Venditte can and can’t do. Reliford believes that ultimately Venditte would have to stick with one arm once an at-bat starts. But what if the batter switches sides during the at-bat. “Good question,” he said. “That’s something that will have to be decided.”
Reliford said that each minor league uses the Major League rules but can modify them as needed. “That’s what the kid’s league will have to do now,” he said. “It’s a very interesting thing.”