Sports games, unlike most other games, allow all possible modes of competition. Depending on the sport and on how many input devices your platform supports, you can offer single-player, competitive, cooperative, team, and league modes; people love to play sports games competitively. Sports games sell far more copies for console machines than they do for PCs primarily because console machines allow many people to play at once in the same room. In addition, console versions can use a TV instead of a monitor on a desk, so all the players have a better view of the action. Because many real sports are played by teams of people, these sports naturally offer opportunities for multiplayer action.
One other competition mode you should consider including is one with no players at all: the computer versus itself. Few other games besides chess games ever implement this mode; after all, people play computer games to interact, not to watch. However, with sports games, people do occasionally like to let the game play itself and watch the results, just as if they were watching a real match on TV. This also allows the computer to play simulated matches that the player doesn't want to play; see the later section "Simulating Matches Automatically."