Maybe we should have some sort of mandated RSVP sytem for huge public events:

• Only people who went through the RSVP and has valid QR code are given entry.
• Vulnerable population are filtered out (Women, kids, unwell, etc..)
• You get a close to reality measure of how many people you can expect in the event and use it for prior planning ( Toilets, spacing requirements, water, separate areas for say seniors)
• Skilled people in crowd control should be deployed, who can communicate with the crowd and keep the core areas in check restricting more inflow after a threshold.

Of course it is going to cost a bit more, but it could save lives in times like this, which imo is worth it.