In baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

, on deck refers to being next in line to bat

Batting (baseball)

In baseball, batting is the act of facing the opposing pitcher and trying to produce offense for one's team. A batter or hitter is a person whose turn it is to face the pitcher...

. In a professional game, the batter who is on deck traditionally waits in a location in the foul territory called the on deck circle.

Being on deck only guarantees the batter will get a chance bat in the inning provided if there are fewer than two outs, and the number of outs plus the number of baserunners adds up to fewer than three. Additionally, the manager

Manager (baseball)

In baseball, the field manager is an individual who is responsible for matters of team strategy on the field and team leadership. Managers are typically assisted by between one and six assistant coaches, whose responsibilities are specialized...

 reserves the right to pull the on-deck hitter for a substitute

Pinch hitter

In baseball, a pinch hitter is a substitute batter. Batters can be substituted at any time while the ball is dead ; the manager may use any player that has not yet entered the game as a substitute...

 at his discretion.

Significance in save situations

A relief pitcher

Relief pitcher

A relief pitcher or reliever is a baseball or softball pitcher who enters the game after the starting pitcher is removed due to injury, ineffectiveness, fatigue, ejection, or for other strategic reasons, such as being substituted by a pinch hitter...

 who comes in to pitch when his team is ahead has the ability to earn a save if the tying run is either on base, at bat, or on deck, and he then finishes the game without giving up the lead.

On-deck circles

There are two on-deck circles in the field, one for each team, positioned in foul ground between home plate and the respective teams' benches. They are technically known as next-batter's circles. The on-deck circle is where the next scheduled batter, or "on-deck" batter, warms up while waiting for the current batter to finish his turn. The on-deck circle is either an area composed of bare dirt; a plain circle painted onto artificial turf; or often, especially at the professional level, made from artificial material, with the team's logo painted onto it.