What is a defensive swing?

A defensive swing can be defined as the batter swinging the bat against a difficult pitch to hit, or in some instances, a pitch that can possibly strike the hitter. In the case of a difficult pitch, the batter is usually just trying to fight off the pitch, make contact, and either foul the ball off or put it in play and home it will find a hole among the fielders.

Protecting the plate. It is fouling off a pitch with two strikes that looks like a strike, but you dont think you can get a hit with it. The purpose of it is to get more pitches, either as strikes to hit, or balls to get walked.