快速球是棒球比赛中最常见的棒球球路。一些强力型投手，像是诺兰·莱恩与蓝迪·强森，都曾投出时速95—103英哩（153—165公里）的快速直球，并靠这个速度来避免球被打击者击中。其他投手投得较慢，但是会在球上做点动作或者尽量投在本垒板的外侧使得打者不容易打到。有时候在球被投出去之前，若能减少打者看到球的时间，也能对打者造成球速上的错觉，这种球路就是爆炸快速球（exploding fastball）：尽管速度不快，但是球似乎很快就到达本垒板了。快速球投出时球通常是逆转前进的，依据马格纳斯效应的理论在球上就会产生一个上升的力量，这就使得球下坠的速度比预期的来得慢。若是在投球时让这种效应更加明显，这种球路就称上升快速球（rising fastball），在打者眼中球就像是会往上飘似的。

The fastball is the most common type of pitch thrown by pitchers in baseball. Some "power pitchers," such as Nolan Ryan and Roger Clemens, have thrown fastballs at speeds of 95–106 mph (152.9–170.59 km/h) (officially) and up to 108.1 mph (174 km/h) (unofficially), relying purely on speed to prevent the ball from being hit. Others throw more slowly but put movement on the ball or throw it on the outside of the plate where the batter cannot easily reach it. The appearance of a faster pitch to the batter can sometimes be achieved by minimizing the batter's vision of the ball before its release. The result is known as an "exploding fastball": a pitch that seems to arrive at the plate quickly despite its low velocity. Fastballs are usually thrown with backspin, so that the Magnus effect creates an upward force on the ball, causing it to fall less rapidly than might be expected. A pitch on which this effect is most marked is often called a "rising fastball." Although it is impossible for a human to throw the pitch fast enough with enough backspin for the ball to actually rise, it does create the illusion of a riser to the batter due to the unexpected lack of natural drop on the pitch. Colloquially, use of the fastball is called 'throwing heat' or 'putting steam on it', among many other variants.