[AtlUmpSteve]

Loose equipment on the field belonging to the defense is covered by 8.5.C (a pitched ball), 8.5.F (using the equipment to catch or intentionally contact the ball), and 8.5.G (a blocked live ball not judged intentionally contacted).

The definition of a blocked ball doesn't differentiate by the location of the equipment; the ruling depends on the type of ball (pitched, thrown, or batted), and the type of contact (intentional or unintentional). The pitcher's mask is no different than the catcher's mask or an outfielder's cap; they are responsible for their equipment if they use it or discard it.