牛棚（Bullpen）是棒球场中投手上场前暖身的区域，也被引申用来指称队上的后援投手群。

该词来自于美国职棒大联盟，是球场边中继投手或救援投手下场之前热身的场地。根据球场的不同，牛棚的位置也有所不同，有些球场是在内野的界外区旁，也有些是在外野区的围墙之后。通常先发投手在先发前也会在牛棚作最后的热身。

牛棚的名称由来最知名的典故是出自于1910年代时，一家名为「Bull Durham」的烟草公司在很多球场的投手练习区上方悬挂着他们的广告看板。而这家公司在当时提供50美元的奖金给能打到看板的打击者，另外，若打者在挂有广告看板的球场击出全垒打，则可获得一盒烟草。1910年时，在近150个有Bull Durham看板的球场中，所有看板共被击中85次，而该公司也发出4,250美元的奖金及超过10,000磅的烟草。而由于投手练习区接近Bull Durham看板及该公司的赞助，加上投手练习区像是圈养家畜的围栏，久而久之，投手练习区便被称作为牛棚。

In baseball, the bullpen (or simply the pen) is the area where relief pitchers warm-up before entering a game. A team's roster of relief pitchers is also metonymically referred to as "the bullpen". These pitchers usually wait in the bullpen if they have not yet played in a game, rather than in the dugout with the rest of the team. The starting pitcher also makes his final pregame warm-up throws in the bullpen. Managers can call coaches in the bullpen on an in-house telephone from the dugout to tell a certain pitcher to begin his warm-up tosses.