In early October, the Tennessee Titans went through the first serious Covid outbreak for the NFL, and the future of the season looked bleak at best. The league gained a serious insight from the outbreak - more precisely defining when individual is considered to be in "close contact" with another exposed individual.
They learned "close contact" could encapsulate individuals who are talking unmasked for any period of time at any social distance. Their findings reiterate the four pillars of transmission - time, distance, ventilation, and masks.
Dr. Allen Sills, the NFL's chief medical officer, found that "if you're failing in two or more of those [pillars], then that's going to become a high risk for a transmission."