The actual interactions between two adversaries in a game vary:
- Boxing, Wrestling
- Absolute competition-- the opponent is the game's presented obstacle.
- Football, Basketball, Soccer
- Direct competition-- a player's performance can be impeded by another player's.
- Tennis, Volleyball, Billiards
- Indirect competition-- one player cannot directly affect his opponent's performance.
- Track and Field, Swimming, Bowling
- Artificial competition-- the game is playable without an opponent.
One step further. In Soul Calibur, players control avatars that execute attacks in order to kill each other. Play from one player can be directly defended against (blocked, dodged, interrupted) by play from the opponent, so this must be direct competition.
Little bit deeper. In Soul Calibur, Taki blocks Amy's 66A, leaving Amy with 5 frames of advantage. Since Taki's fastest attack (A) would impact in 10+5 frames and Amy's fastest attack (6B) impacts in 11, it is now Amy's turn to attack. Amy attacks with 3BA, which Taki blocks, leaving Taki with 11 frames of advantage. It is then Taki's initiative. Since these players are taking turns playing, this must be indirect competition.
The main difference between video games and sports is the physical barrier of entry-- there are very few people in the world that can serve a tennis ball at 140 miles per hour, but anyone with fingers will be able to press the buttons to score Taki's A+K, B+G air throw. But since the difference between the elite and the newbies is so relatively small, it is curious that the game play of video games changes so drastically based solely on the level of competition.
And this is not even considering the advent of artificial intelligence...