A comparison of the differences between baseball and softball can be made as softball is directly descended from baseball. An observer of one game would find the other very similar, but there are several important rule differences.
Fastpitch softball is more popular in competitive leagues, especially at the college and international tournament levels, while slow pitch is more popular in recreational leagues where the relative skill levels of different players may vary widely. The different rules of slowpitch can be viewed as maintaining a competitive balance for less skilled players by eliminating certain strategies (e.g., base stealing and bunting) which require a high level of skill to counter. Additionally, recreational leagues may impose their own ground rules, either for competitive balance or to meet local constraints (e.g., a time limit may be imposed on a game to ensure multiple games can be played in one day).
A regulation softball is significantly larger than a regulation baseball. A softball measures between 11.88 and 12.13 inches in circumference and weighs between 6.25 and 7.00 ounces; a baseball measures between 9.00 and 9.25 inches in circumference and weighs between 5.00 and 5.25 ounces.
Variable distance from home plate is mandatory in professional and university leagues and optional in youth leagues. Many youth leagues, such as Little League, use a constant distance from home plate.
Variable distance from home plate, depending on the individual field. (maximum of 250ft (76m))
Constant distance from home plate, although some less organized leagues have no fences.
Pitching distance
60feet 6inches (18.44m)
Varies by level: 40 feet (12m) (youth), 43 feet (13m) (adult women) or 46 feet (14m) (adult men)
Raised sloping mound, radius of 9 feet (2.7m), maximum height 10 inches (25cm)
Flat circle, the radius of 8 feet (2.4m), marked with a white chalk circle
Pitching rubber only
Players
Fielders
Nine
Nine
Ten (fourth outfielder)
Extra player
A designated hitter (DH) may bat in place of a pitcher (rule varies by league; some levels allow DHs for other fielders)
One designated player (DP) may bat in place of a fielder.
Some leagues allow an arbitrary number of extra players, up to the entire roster.
Substitution
No player substituted for may return to the game, including the replaced player if the DH takes a defensive position. Under high school rules in the United States, a player may be substituted for and return to the game once. A pitcher who leaves the game may return, but only as a fielder (not the pitcher or DH).
Free defensive substitutions, provided each player occupies the same position in the batting order. If the DP takes a defensive position, the replaced player cannot return to the game.
Free defensive substitutions, provided each player occupies the same position in the batting order.
Runner is usually permitted to take a lead after the ball leaves the pitcher's hand, but must return to base between pitches if the ball is not put into play. The runner can be called out for taking a lead before the pitch.
Pitching
Delivery
Any method; in practice, usually overhand.
Underhand; no speed or arc restrictions.
Underhand; must travel in an arc and within certain height restrictions (a common range is between 6 and 12 feet (1.8 and 3.7m) above the ground). Umpire can call a pitch "illegal" while in flight.
The ball remains live. If the batter reaches base successfully and all runners advance, no penalty; otherwise, the play is negated, the pitch attempt is automatically a ball and runners advance one base.
The ball remains live. If the batter does not swing, the pitch is automatically a ball.
