People who watch sports often hear about how the high-altitude of Colorado affects sports and sports performance. Some athletes actually go to Colorado in the off-season to train in hopes of reaping some of the benefits of high-altitude training.
One way that playing sports in high-altitude affects the game is endurance. Players who are not accustomed to playing under such conditions can have some endurance issues. The home team will usually have the advantage because they are used to the conditions.
Baseball is affected by play in Colorado. When the ball is hit, it will travel further. Players are more likely to hit home runs when they play in high-altitude ball parks. This can clearly affect the score of a baseball game.
Sports like football and soccer can also be affected. Not only from the effects of the altitude on the players, but from the effects of the altitude on the ball. When kicked, the soccer ball will travel through the air differently. This can throw some players off. Goalies can misjudge block attempts. The football also travels through the air slightly different. Field goals are also easier to kick.
As you can see, playing in high-altitude conditions clearly does affect sporting competition.