Opposite field is a baseball term.

Most batters when batting tend to pull the ball - that is, they will push the ball in the direction their bat is headed, across their body. For a right handed hitter, this would be from right to left, and for a lefty, left to right.

Thus, "opposite field" is the opposite of this - rightfield for a right-handed batter, and leftfield for a left-handed batter.

Opposite field hits are fairly rare, because it requires the batter to swing slightly later than normal, which more often than not results in a foul ball.

Hitting to opposite field is a pretty simple concept for the batter:

• Stand closer up in the batter's box and farther away from the plate. This will make all incoming strikes slightly quicker, resulting in a slightly later swing than normal.
• As you swing, keep your back foot stationary and step towards the opposite field. This will shift the weight of your bat and body towards opposite field, helping with direction.
• Choke up slightly on the bat. This will prevent a lot of uppercut pop ups to the shortstop.

Good luck, and play hard!