From 1955 through 2009, 128 American football players died due to hyperthermia while participating in football activities. This study uses BioKlima, a biometeorological model, to examine the microclimates of five of these cases at five-minute intervals in an effort to determine what factors led to each player's death, in addition to assessing the performance of three different perceived temperature indices on predicting safe practice conditions. Meteorological data used to set conditions within the model are obtained from the National Solar Radiation Database hourly data and interpolated to five-minute intervals. Wet Bulb Globe Temperature (WBGT) was the most consistent metric in assessing dangerous conditions on the football practice field, when using guidelines established by the American College of Sports Medicine. All five cases reached the WBGT threshold where football activities should have been cancelled in order to keep players safe. All five players also remained above the hazardous threshold for sweat loss in a non-acclimatized player, indicating that the players were dehydrated when they suffered from hyperthermia. In all five cases, players could not maintain their own internal heat load because of exertion, and lost the ability to maintain their own internal temperature. Communication of the short timescale during which conditions can become hazardous to players should allow for better scheduling of practices early in the season, and encourage coaches to keep a closer watch on players for the signs and symptoms of hyperthermia.