[quote name='puddytay']A general rule sports games are never considered rare or valuable.[/quote]
Actually some of the rarest games for modern systems are sports games:
Genesis: Madden Football Championship Edition
Gamecube: NCAA Basketball 2K3
Granted sports games come in 2 categories of rarity... Ultra Common or Ultra Rare.
But Home Run King isn't a rarity at all, but it's great if you want to hear "Now Batting, #29 Kansas City Royals, MIKE SWEENEY!"