Ace | refers to a team’s best pitcher, though it can also be used to describe an elite pitcher in general. Therefore, a team with multiple elite pitchers is said to have more than one ace.

Appeal Plays | the defensive team can appeal certain plays to alert the umpires of infractions that would otherwise be allowed without the appeal. 

Balk | is an illegal act by the pitcher when one or more runners are on base.

Batter’s Box | A regulation baseball field has two batter’s boxes — one on the left side and one on the right side of home plate.

Catcher’s Interference | the batter is awarded first base if the catcher (or any other fielder) interferes with him at any point during a pitch.

Can of Corn | a routine fly ball hit to an outfielder.

Collision at Home Plate | the baserunner is not allowed to deviate from his direct path to initiate contact with the catcher (or any player covering the plate).

Dead Ball | is a ball that is out of play.

Fair Ball / Foul Ball | the foul lines and foul poles are used to demarcate fair territory and, thus, determine what constitutes a fair ball.

Force Play | occurs when a baserunner is no longer permitted to legally occupy a base and must attempt to advance to the next base.

Infield Fly | any fair fly ball (not including a line drive or a bunt) which can be caught by an infielder with ordinary effort when first and second or first, second and third base are occupied, before two men are out.

K | a strikeout.

Obstruction | an act by a fielder, who is not in possession of the ball or in the process of fielding it, that impedes the baserunner’s progress.

Pickle | a rundown.

Southpaw | a left-handed pitcher.

Strike Zone | is the area over home plate from the midpoint between a batter’s shoulders and the top of the uniform pants, when the batter is in his stance and prepared to swing at a pitched ball, and a point just below the kneecap. In order to get a strike call, part of the ball must cross over part of home plate while in the aforementioned area.

Walk-off | any offensive play that gives the home team the lead, and thus, the win, in the bottom of the last inning.