"The Brady Effect" could apply to a lot of things. It could apply to how the Tampa Bay Buccaneers went from a middling team for the past decade to a Super Bowl champion in 2020-21, thanks to the arrival of Tom Brady. It could apply to how the New England Patriots went from a perennial division winner in the AFC East to a 7-9 team, thanks to the departure of Tom Brady. It could apply to baseball players who randomly have a 50-HR season out of completely nowhere, like the 1996 iteration of Brady Anderson, only to sink back into a mediocre offensive display for the remainder of their careers... but I would cautiously assume that this is probably not the most popular usage.
In the case of Fanatics executive chairman Michael Rubin, "the Brady Effect" applies to Tom Brady in an off-the-field sense: merchandise sales. Though Brady wasn't the only big-time acquisition for the Buccaneers' 2020 season — Rob Gronkowski, Leonard Fournette and Antonio Brown all count there, too — he certainly seems to be the primary factor in the absolutely massive increase in team sales on Fanatics.
The biggest YOY increase in the history of the company?! I guess it shouldn't be that huge a surprise, considering the fact that Brady seemed like a Patriot for life and was then pretty damn successful once he chose the other route. Still, I'm surprised that, for instance, the league-shaking 2018 acquisition of Nathan Peterman to the Raiders didn't blow up Las Vegas' sales. In all seriousness, I have to wonder if the Jaguars' team sales even approach a quarter of that Brady-based YOY increase with new quarterback Trevor Lawrence in town.
Fanatics may see an increase as a whole ahead of the 2021 season for a whole different reason, and it's one about which Brady isn't too excited.