The opposite field refers to right field for a right-handed batter and left field for a left-handed batter. Most batters will tend to be natural pull hitters, meaning they will hit most pitches, towards the field on the side of home plate where they are standing; this is how one hits a ball with power, and most home runs are hit to the natural field. However, when a pitch is thrown on the outside part of the plate, an attempt to pull it will often result in a weak ground ball. Instead, a smart batter will push such a pitch towards the opposite field, where it is more likely to fall for a hit. Derek Jeter, for one, is a master of slapping such pitches to the opposite field for base hits.
Some contact hitters will also deliberately hit any pitch to the opposite field by using an inside-out swing. Even if a ball hit in this manner will not go as far as one hit with a full swing, this forces the defense to position its players in a much more conservative fashion, opening up larger gaps between players. In contrast, a player who insists on pulling every pitch while going for maximum power, what is known colloquially as a "dead-pull hitter", will often face a defensive shift that reduces his chances of hitting the ball safely.
For decades, only the very strongest hitters could hit a home run to the opposite field. This changed in the 1990s, as the spread of muscle-building exercises and steroids allowed many more such homers.