I think they stopped doing that after there was a tragedy at some structural collapse where a lot of people were killed.
Mechanical Resonance? Where if the people are bouncing at just the right frequency it amplifies the vibrations.
Yes-I can’t remember...perhaps it was not some stadium collapse, instead, I may have been thinking of the Hyatt walkway collapse in 1981, and that wasn’t due to mechanical resonance, it was just a poor design.
But I think that game I went to was only days after that collapse, so while it may not have been at the front of everyone’s mind, it was most certainly at the back of their minds which explains the instantaneous stop of the jumping and stomping of feet when someone yelled out at that Boston Bruins game in the old Boston Garden.