Tom Brady and Patrick Mahomes function within the same general constructs that have governed the N.F.L. for more than a century — playing on a field measuring 360 by 160 feet, accompanied by 21 other players, trying to gain 10 yards in four downs.
Their approaches, though, are a gulf apart, with each quarterback at the pinnacle of styles that define the modern offensive era. Brady, 43, is a pocket passer extraordinaire, an archetype that is waning as teams try to build around dual-threat quarterbacks like Mahomes, 25, who can lead the dynamic offenses that have reimagined how football is played in 2021.