It isn't easy to pitch in Denver. The high altitude and dry air cause the ball to travel farther - on average, a ball at Coors Field will carry 20 feet more than at an average ballpark - and pitches have less movement. The Colorado Rockies have finished dead last in the National League in runs allowed 19 times since they came into the league in 1993, and have never finished higher than seventh.
This year is no different, with the Rockies not only dead last in baseball in runs allowed, but a full 0.