布局投手（Setup man/pitcher，简称：SU）是接替在先发投手或中继投手之后，终结者之前，通常是在第八局上场。

由于目前中继投手开始使用中继点或是中继成功(hold)，因此在领先三分内且于第八局上场的布局投手通常是该队赚取中继点最多的投手。

布局投手通常是球团有意栽培为终结者的年轻投手或是退出终结者位置的老将，因此他们在实力上面通常是牛棚战力中次强的投手，故若终结者身体不适或受伤时，有时也能胜任代班终结者的位置，因此可视为终结者的备胎人选。

一支球队通常有左右各一的布局投手。

在美国大联盟，知名的布局投手为费城费城人老将Tom Gordan、洛杉矶道奇的郭泓志、波士顿红袜的冈岛秀树，及底特律老虎队的祖马亚(Joel Zumaya)等。

In baseball, a setup man (or set-up man, also sometimes referred to as a setup pitcher or setup reliever) is a relief pitcher who regularly pitches before the closer. They commonly pitch the eighth inning, with the closer pitching the ninth.

As closers were reduced to one-inning specialists, setup men became more prominent. Setup pitchers often come into the game with the team losing or the game tied. They are usually the second best relief pitcher on a team, behind the closer. After closers became one-inning pitchers, primarily in the ninth inning, setup pitchers became more highly valued. A pitcher who succeeds in this role is often promoted to a closer. Setup men are paid less than closers and mostly make less than the average Major League salary.