Ask them politely to lower it. If they don't, you have two options:
A. Leave your seat to go find a security guard, missing part of the show in the process and potentially having this person fuck with you for the rest of the show in retaliation.
B. Rip that shit straight out of their hands and toss it to the lower arena. They'll have no idea who did it because their view was blocked by their umbrella. Don't have to miss a second of the show.
Rip that shit straight out of their hands and toss it to the lower arena. They’ll have no idea who did it because their view was blocked by their umbrella. Don’t have to miss a second of the show.
The poor sobs who got their head smacked with a thrown umbrella wouldn't know who did it either.
I usually just articulate to them exactly the messed up the thing is that they are doing in a way that they have to aknowlage it. Then they have a choice, they can either say oh, I'm sorry I didn't mean to do that and fix it. 99% of people don't like having to aknowlage they are an asshole. They would rather you think they are stupid, not an asshole. OR, they say suck my balls and do it anyway. At that point all options are on the table.