A few decades ago, the average major league game was only 2:30 - not short, but not really long, either. Now it's past 3 hours, if memory serves.
Ironically,a lot of that has been because of TV - your single game of the week and a few dozen local games have been replaced by gobs of games everywhere, meaning more commercial timeouts, more players grandstanding and taking time between pitches, etc..
Also more relievers and coaching visits have hurt, too. Along with higher scoring; the '70s and'80s were excellent for baseball speed yet, it doesn't have to be the dead ball era type of the '60s.
My answer to the challenge to destroy American football (starting with the Steelers keeping Unitas) would be a start. I invented a play that caused a player's death, not knowing of the Gifford concussion; I just read about that, wow. It was in 1960, so would have caused a big stigma, yes. I thought having it later, in a Super Bowl equivalent, would have more impact but the 1960 one could work, too.
You then have to have some way to keep baseball going on TV without the longer breaks for commercials, but I don't know how. Signs ont he outfields in the '60s and '70s parks like int he old time ones can only do so much.
But, if the 1960 hit does kill, perhaps that butterflies away the genius of NFL Films - I have in that challenge response a World Series being covered instead. It would be better as a season, though, or something to cause a ball club to see the great value of the marketing of the sport.
Because, one of the problems, as someone put it back in the late '80s,w as that for many years, "Baseball's marketing strategy was to say, 'We're the national pastime - come watch us.'" Whereas, a forward thinking man could have done some wonders.
Hmmmm, there was that crazy debacle of a Commissioner in 1965 after a lot of dithering and compromising. Maybe if Rozelle, not the first choice, doesn't get hired baseball could tap him?