[gyroscopeRaptor]

Is the only justification for footballs we have the nebulous "alternating sports years" pattern?

Footballs would be a hard game piece in the goals. An AimHigh high goal would likely jam often, Breakaway low goals would have no way of returning to the center like Breakaway's soccer balls, any center goal would be easily "camped" with a quick return (think 469 only more effective) and still be susceptible to jams, and side goals where Lunacy outposts were would be still worse.

Before you say "they haven't been used," look at those reasons and consider why the GDC hasn't made them yet. Remember, plenty of other pieces haven't been used in a few years. We could just as easily use stacks or tetras.