Is a check swing a strike in the rule book?

Answer 1

Incredibly, neither the Baseball rule book nor the umpires' manual contains a written definition of a check swing. The generally accepted rule of thumb is that you need to break the plane of the front of home plate with your wrists and at least part of the barrel of the bat. But because there's no actual definition, in practice a check swing is whatever the home plate umpire says it is.

AnswerIt's extremely subjective; each umpire has his own guidelines. Some will call a strike if the wrists break, others will call a strike depending on how far the bat goes, and still others go by whatever they judge the batter's intent to have been. AnswerUmpires should address this as a judgment call, based on whether or not the feel that the batter intended to offer at the pitch.

Answer 2

The rulebook says a strike is a pitch struck at by the batter and missed. It's up to the umpire's judgment as to whether or not the batter swung or not.