Coors Field Affects Pitchers

From Clay:

So, my cousin plays baseball for a Toronto Blue Jays minor league team. His ERA last year was 5.40. I looked up what ERA meant in Wikipedia. After an explination there's a paragraph about Coors Field and how pitchers hate it:

ERA, taken by itself, can also be misleading for starting pitchers, though not to the extent seen with relief pitchers. ERA is affected to some degree by the park in which a pitcher's team plays half its games. For an extreme example, pitchers for the Colorado Rockies face a double problem.

The high altitude of Denver causes fly balls to travel up to 10% farther than at sea level and reduces the ability of pitchers to throw effective breaking balls.

Also, Coors Field has fences that are not long enough to compensate for the increased fly-ball distance at Denver, plus a relatively small amount of foul territory. In modern baseball, Sabermetrics utilizes several Defense independent pitching statistics to try to measure a pitcher's ability independent of factors outside their control.