Despite the big Mayweather Pac PPV, when did the popularity of boxing as a mainstream sport decline in US? My guess: around mid 2000s, say 2004-06
Tail end of the 90's early 2000's the big drop was starting. Mayweather, De La Hoya, Jones and Pacquiao kept it going for awhile, but not having a first rate heavyweight prospect, coupled with the death of boxing in schools and gyms, had it significantly declined already from the Tyson-Holyfield-Bowe days already.
Boxing began losing TV dates somewhere in the 1990s or early 2000s, which made it harder to create a market for the next generation of stars. Even challengers to the stars who could have developed followings with weekly TV or network exposure became instead complete unknowns to the public. The rise of MMA stole a lot of boxing’s thunder with a younger generation who wanted more of a bloodlust fix. And that (drawing the next generation of talent into the octagon instead of the ring) plus rising awareness of CTE reduced the talent pool of people even taking up boxing in the first place. A few generations of young athletes grew up wanting to become Muhammad Ali. Then as he aged and his condition worsened, the next generations grew up not wanting to end up like Muhammad Ali.
A long, long time ago. When you consider boxing was the most important sport in the USA along with Baseball. It started losing popularity in the early decades of the 2nd half of the 20th century.
Probably what most of posts have said. Early 2000s. Popularity wise, boxing is at its peak when the Heavyweight division is booming like in the 90s. After that, Oscar, Pacquiao and Floyd kept it afloat but the sport overall was still declining. Today it's even worse.
American HWs carried boxing there pretty much from the 1960s to the 1990s until the Klitschko era. UFC didn't help either, nor having Wilder who was an overprotected borderline fraud to some extent.
For reference I am turning 35 this year. I would say I was one of the few boxing fans of the kids I grew up with and went to school with. I played multiple sports and rarely did other kids watch or follow the sport. There was interest in the Mayweather-De La Hoya fight and I remember most of the kids who watched it thought it was a dud. Mayweather-Pacquiao caught interest among the kids that watched Sports center and loosely followed the sport. That fight did more damage by the wait and then the let down. There was some cross over interest in the Mayweather-McGregor fight but I think that mostly stemmed from Floyd being a great salesman and Conor's cross over appeal mixed with MMA's rise Kids in their young twenties at work follow UFC religiously but through combat sports familiarity know a little about boxing. I think this is very different from my father's generation, born in 1956 where everyone knew boxing and idolized Ali and then got the four kings. And he would tell me about my grandfather born in 1927 and his stories about Randy Turpin and Rocky Graziano. I'd say it slowly declined from the 70's or 80's from its peak and then slowly declined from there. I only have one friend that watches boxing so I no longer do fight parties like I used to and if I go to a fight I go solo