Infield - The area of the field that is located nearest to home plate. There are six positional players in the infield: first baseman, second baseman, third baseman, short stop, pitcher, and catcher.

Infield Fly - An infield fly is any fly ball that is not a line drive or bunt that is considered an ordinary catch for the fielder by the umpire. When the umpire calls the hit an infield fly, the batter is automatically out. This rule applies when there are runners on first and second or first, second and third before two are out.

Infield In - The strategic defensive action of playing the infield closer to home plate than normal. This is usually done with a runner on third and less than two outs. The objective is to place the defensive player closer to home so that the player can throw the runner out trying to score.

Infielder - Any of six defensive position in the infield that includes the first baseman, second baseman, shortstop, third baseman, catcher, or pitcher.

Inning - The period of the ball game that allows for both the offensive and defensive players to bat once. While one team is batting the other team is fielding. There are a minimum of nine innings per game in Major League Baseball and normally 6 innings per game in Little League Baseball. The number of innings maybe shortened by the umpire if required for weather conditions.

Inside The Park Home Run - A home run where the offensive player bats the ball inside of the baseball field.

Intentional Walk - The defensive strategy of giving a base on balls to the batter. In certain strategic situations, it may be advantageous for the defensive team to intentionally walk a batter to set up the double play or to pitch the next batter in the line up.

Interference - The unexpected interruption of play by either a player or spectator. There are four types of interference that can occur during a ball game: 1) Offensive interference is when the batting team obstructs, interferes, hinders, or confuses the defensive team. If the umpire calls offensive interference, the batter or runner shall be out. All other runners must return to the previous base before the interference was called. 2) Defensive interference is when the defensive team hinders or prevents the batter from hitting the ball. 3) Umpire interference is when the umpire hinders or prevents the catcher from throwing out a runner trying to steal a base or when the ball touches the umpire in fair territory. 4) Fan interference occurs when a spectator touches a live ball in fair territory. In all instances, the ball is considered dead.

K - Another term used for a strike out.

Knuckle Ball - A ball thrown by the pitcher that has an unpredictable path to the catcher. The pitch is so called because the ball is thrown with the knuckles placed on the ball rather than the finger tips. The pitch is considered difficult to throw for strikes and for that reason it is not used a lot in professional baseball. Because of the unpredictability, it is difficult to hit as well. Pitchers such as Phil Neikro of the Atlanta Braves in the 1980's have made a career out of throwing the knuckle ball with success.