I think footballs also.
The 8 1/2" Power Spiral Football that is on
Http://www.pooftoys.com/ are very durable. They actually have some low plastic coating on them that stops them from coming apart. (doesn't it bring back the little kid days).
Those slinkys would break/snap way to easy and would cost first way to much to repace 1-2 every match
Next think we should think about is surface?? Grass????? Artificial Turf???