[9YearLurker]

What specification did they violate?

Sounds to me like the same geek advantage teams have been getting out of stats is here being applied to the equipment.

[Teacher317]

MLB Rule 3.02 states: “The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches in length. The bat shall be one piece of solid wood.”
Further, experimental bats cannot be used “until the manufacturer has secured approval from Major League Baseball of his design and methods of manufacture.”