Maybe it's some kind of "breakthrough of the repressed": fans have repressed anger of being caught in the dynamic pricing system and they consider that since they have paid so much of their sparse money to see so-and-so on stage they have the right to behave any way they please. It's totally wrong and inexcusable in any case. Throwing hard objects at someone is considered an assault in real life and should be considered as such in that context too.
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"Won't you give me all the speed I lack?" - The Clash
ASD-1, PTSD. AQ 39 / Ritvo 145 / ADI-R: all 4 sections above threshold