“Altitude sickness typically occurs only above 2,500 metres (8,000 ft)” “AMS occurs in about 20% of people after rapidly going to 2,500 metres (8,000 ft) and 40% of people going to 3,000 metres (10,000 ft)” less than 1% get it at Denver’s altitude, that would mean 5 people in entire football roster.
I live in the biggest city in this continent, México city, with 20 million people, and I don’t mean the people that live here, the 6 million tourist that come here every year, only a very small percentage gets altitude sickness, And here there are more professional teams of all sport than in any city in your country, and non of them is undefeated.