Why isn't the ball used in football called "a football ball"?

We know that you need a ball to play cricket, golf, or tennis, and we refer to the balls used in those sports as "cricket ball", "golf ball" and "tennis ball" respectively: you take the name of the sport and then add the word "ball".

But as "football" is the name of the sport itself, why isn't a football referred to as a "football ball"? The same applies to "netball ball", "basketball ball" and "volleyball ball" of course.

Solution 1:

Your question implies that football properly describes the game and, by extension, the ball itself. I wasn't sure, so I checked and it is indeed the case historically. Etymonline says:

football
open-air game, first recorded c. 1400. Forbidden in a Scottish statute of 1424. The first reference to the ball itself is late 15th century.

So, usage of the term to refer to the ball instead of the game is quite old, but it still took more than a century after the name of the game was established. Nothing is said of the reasons we don't say “football ball”, so I assume that it was the obvious: to avoid unwarranted repetition.

Solution 2:

I think we don't say ball twice because it would be redundant to do so.

The name of the game lets you know that you are playing a ballgame, a pastime that requires one to put a ball in motion.

So we just name the ball with the game name to show that a specialized ball appropriate for that game is needed to play it.

Solution 3:

In reading the question, I realized that in basketball, football (American and English), volleyball, the ball is virtually the only equipment (ignoring safety equipment) that is used. Whereas in golf, tennis, cricket there is always another critical component, i.e., club, racket, bat.

(An exception to this would be the game of baseball.)