The fastball is the most common type of pitch thrown by pitchers in baseball and softball. Its distinctive feature is its high speed. "Power pitchers", such as former major leaguers Nolan Ryan and Roger Clemens, relied on the speed, often exceeding 100 mph (45 m/s), and movement of their fastballs to prevent the ball from being hit. As an alternative to the fastball, pitchers can put more movement on slower thrown balls, or throw them towards the inside or outside of home plate where batters cannot easily reach it.

Fastballs are usually thrown with a backspin so that the Magnus effect fastball creates an upward force on the ball. This causes it to fall less rapidly than expected, and sometimes causes an optical illusion often called a rising fastball. Although it is impossible for a human to throw a baseball fast enough and with enough backspin for the ball to actually rise, to the batter the pitch seems to rise due to the unexpected lack of natural drop on the pitch.

Colloquially, a fastball pitcher is said to throw "heat" or "high cheese” among many other variants.

Many varieties or 'shapes' of fastballs have been described throughout baseball history, including four-seam fastballs, rising fastballs, two-seam fastballs, sinkers, running fastballs, cut fastballs, and split finger fastballs. However, MLB currently recognizes three distinct types of fastballs, each with substantial variety in terms of movement, consolidating the numerous antiquated descriptors into three groups: four-seam fastballs, sinkers (two-seam fastballs), and cutters (cut fastballs). Despite its name, the split-finger fastball or 'splitter' is not considered to be a type of fastball and is known as an off-speed pitch.

The four-seam fastball is the most common variant of the fastball. The pitch is used often by the pitcher to get ahead in the count or when he needs to throw a strike. This type of fastball is intended to have minimal lateral movement, relying more on its speed and vertical "rising" movement. It is typically the fastest pitch a pitcher throws, with recorded top speeds above 100 mph (45 m/s). Two general methods are used to throw a four-seam fastball. The first and most traditional way is to find the horseshoe seam area, or the area where the seams are the furthest apart. Keeping those seams parallel to the body, the pitcher places his index and middle fingers perpendicular to them with the pads on the furthest seam from him. The thumb then rests underneath the ball about in the middle of the two fingers. With this grip, the thumb will generally have no seam on which to rest.

The four-seam fastball is widely regarded as the main key to advancing to the next level of play. One of a baseball scout's main criteria when scouting a prospect is how fast he throws a four-seam fastball.

The sinker, synonymous with the two-seam fastball, two-seamer, tailing fastball, or running fastball is a type of fastball thrown with a seam orientation that induces more downward or arm-side horizontal movement compared to four-seam fastballs or cutters. Historically, distinctions have been made between these terms, but today, they are all recognized by MLB as variations of the same pitch. Differences in arm slot, spin, and velocity cause some sinkers to exhibit more vertical "drop" or "sink", while others "run" or move more horizontally toward the pitcher's arm side. The unique running and sinking movement profile of the sinker makes it more likely to induce ground balls than other pitches as it sinks under the plane of the batter's swing. Not all fastballs exhibiting sinking or running movement are necessarily sinkers; four-seam fastballs thrown from a low arm slot can also exhibit sinking and running movement due to the horizontal spin axis imparted by a low or sidearm release point.

To throw a sinker, the pitcher typically grips the ball as they would a four-seam, but with their index and middle finger parallel to the seams instead of perpendicular to them. This causes the ball to spin with two seams crossing the plane of spin instead of four.