unfortunately it's not the first or second time I've seen that sort of stuff. I've heard spit just rains down sometimes... I'm recalling a slo-mo video of a female Warriors fan spitting on Trailblazers following a loss.
You know how they raise a net behind the goal posts when a field goal is being tried? They should have the same sort of setup protecting the tunnel entry to knock down most of the projectiles. It seems like a simple enough solution to lesson this sort of BS