So this from the NFL's top doc. It's the SYMPTOMATIC driving the spread, not the other way around.
www.espn.com
NFL chief medical officer: Symptomatic players driving COVID-19 spread; no indications of asymptomatic spread

NFL: Symptomatic players driving COVID spread
The NFL is basing its new COVID-19 protocols on data that shows the virus is being spread overwhelmingly by symptomatic individuals.