There has been a lot of talk about defensive shifts in baseball. But what is one? Well, a picture says a 1,000 words, so here you go.

Clearly, the batter hits to the right. The fielders have all come over. Much like when you have a flooding problem, you put sandbags where the water is coming up.
Another view of the shift below

Look at the left side. Nothing! To be an effective hitter, you have to use the whole field. You cannot be so predictable that a shift can be used on you.