Nicktoons MLB

When you have a person with 2 strikes, press and holding RT. You will see the screen zoom in and turn a yellowish tint. Then pick a location (I usually stick to the corners) and a pitch (stick with a fastball or whatever pitch is 4 stars) and throw it. If the player swings and misses or doesn't swing at all and its a strike, you will see the achievement pop immediately.

This shouldn't be too hard and you will likely get it without even trying.