Sports Authority Field at Mile High doesn't have that name for just any reason.  Home to the Denver Broncos, it is exactly one mile above sea level and is surrounded by the thinnest air in the NFL.  As far as football goes, thin air really benefits the home team in many more ways than expected.  Other than the obvious facts that kicks and passes go farther, daily practice at that elevation can make a football team extremely effective when it comes to the physical side of the game.  When the Broncos are away, the thicker, more oxygen-rich air they play in only makes them a better, more effective team that is seemingly better conditioned than their opponents. These conditions work well for football, but not so much for the very different game of baseball.  

Coors Field, also in Denver is home to the Colorado Rockies, who unlike the Broncos, are not known for their league- dominating defense.  In fact, despite larger fences and a deeper outfield, Coors Field is known as a hitter- friendly park, or in other words, a park that makes it easy to hit home runs.  Now one may say that occurrence is due to the simple fact that less air means less drag and therefore farther flight, but those people are mistaken.  This truth has to do with everything that happens before the batter hits the ball, and even before the stadium itself was constructed.  The architects who designed Coors Field were very much aware of the fact that balls would carry farther in the thin air of Denver.  To combat this, they pushed the outfield fences back well past the average distances to left, center and right fields.  Because of this move, the designers created the largest outfield in the MLB, and with it, the most area for outfielders to cover.  This creates many prime landing spots for balls hit by opposing teams.  Its also worth mentioning that the longer fences weren't really long enough, and since its first game,  Coors Field has had a very strong "hitter- friendly" reputation.  

Now architecture is all well and good, but some may still ask: what does this all have to do with physics??  The answer lies in what happens to the baseball in this high elevation and large outfield.  Before the game is even started, a shipment of official MLB balls are received and stored in a room separate from both teams (and safe from any Boston players with air pumps from their favorite NFL team) until the umpires and stadium officials take balls as needed for the game that day.  Sitting untouched at such a high altitude actually dries out the balls and makes them denser than normal (because of the low humidity at high elevation).  This denser version of the ball is prime material for hitters, as it is more responsive to the force sustained from the bat and will travel much farther than a more moist ball.  Humidity aside, from the second the ball is released from the pitcher's hand, the defense is put at yet another disadvantage.  As I've covered before in a previous post, airflow over a baseball and the Magnus Effect dictate the direction and severity of the "break" (curve/ movement) in a baseball.  With less actual air in the space around the ball, there will be less interacting with the seams, meaning less overall movement of the pitch and therefore a much easier pitch for a hitter to drive over the fence.  Then of course, when the ball is in the air, less air density will offer less resistance to the flight of the ball and through all of these factors, baseballs fly out of Coors at a very high rate.  

Since the construction of Coors Field, many studies have been done on the effects thin air on baseball and as a result, humidifiers have been added to baseball storage rooms at Coors.  This has actually helped reduce the amount of home runs but this thin air, coupled with the so-so skill of most Colorado players (sorry Rockies fans) makes a very unfortunate combo that calls into question the true meaning of "home field advantage".