Safety baseballs are designed for very young players from age 4 to 8 in starter leagues such as tee ball. They are noticeably soft on the surface compared to other types of balls and are lighter. Safety baseballs are inexpensive and usually built entirely of man-made materials. They are designed for small lightweight aluminum bats.
Reduced Injury Factor Baseballs
Reduced Injury Factor baseballs are higher performance than safety baseballs, but have a poly core and are softer than a regular youth hardball, reducing the risk of injury. RIF baseballs are available for different age levels, and are often used for practice.
Youth Tournament Baseballs
Youth league baseballs have a cushioned cork center and are wound less tightly than balls designed for adult play, but they're not soft. Youth league balls are designed for experienced baseball players from 8 to 14 and are used in Little League tournament play. A youth tournament ball may have a leather cover and wool windings on the inside. They are designed for youth-sized aluminum bats.
High-School and College Baseballs
Baseballs used at the high-school and college level are similar to professional-grade baseballs, but have a slightly lighter density and are designed for aluminum bats, not wood. They are usually made with a cork core, wool windings and a leather or high-quality synthetic cover.
Major and Minor League baseballs are the densest and highest-quality balls made. They have a high-grade leather cover and rolled seams that are neither flat nor raised. They are designed for wood bats. Official baseballs are a requirement in major, minor and some other leagues.
Players on all levels may use inexpensive balls made with lower-quality materials for practice. Though they are lower in performance, these balls can be cheaply replaced if lost or worn out.