Air Pressure
Air pressure is the weight of all of the air above the height of observation. The altitude of a location also affects the air pressure. In high places, like mountain regions, air pressure is less. This lower pressure reduces the amount of lift and drag on the ball, allowing it to go farther.
A prime example of this phenomena occurred at Coors Field in Denver, Colorado. The field has an elevation of 5,200 ft., the highest stadium in the league. When the park was under construction, designers knew that the lower air pressure would lead to baseballs traveling longer distances. The fences back were pushed back at the park, to prevent an increased number of home runs, thus creating one of the largest outfields in Major League Baseball (MLB).
The high elevation can also impact a player’s performance if they athlete has not had time to acclimate to the thinner air and can find it hard to breathe.