Balls are a mysterious invention, in that we really are not aware of their inventor or origins.
Balls have been around for millenia and have entertained generations and provided a relatively simple and inexpensive device to be used in a wide variety of competitive activities.
Balls are used in professional competitive sports as well as backyard activities all over the world, by both young and old players alike.
Balls are used in nearly every competitive team sport.
Balls also come in various sizes, weights and shapes, with varying textures, made or different materils and used in different type of actions, using widely varying rules or each game or contest.
Balls used in professional competitive contests have strictly regulated characteristics, ranging from size, shape, weight, texture, inflated pressure and even colors.
Balls used in amateur back-yard games are not regulated and are simply comforming to accepted standards as for size, weight, and internal pressure. These characteristics do very to some extent and the sellers of these items pretty much control what kind of balls are available for sale in any specific area.
Balls range in size from table-tennis (ping-pong) to bowling balls.
Table-tennis balls are probably the lightest available anywhere with also the highest internal pressure there is.
Bowling balls are likely the heaviest available anywhere, also with the highest permanent pressure, since the are completely solid-core using a heavy substance internally.
Many other types of balls are in between the above mentioned two, namely:
Water polo balls
Footballs (the only ball that is not round, rather oval)
Plus there are many regional games using balls of verying characteristics that are not known to the entire world)