Why was traffic disastrously bad tonight around downtown?

I don't live there, but happened to drive downtown tonight (Sunday) around 10pm to go to Whole Foods. After about an hour trying to drive a few blocks and finding multiple roads closed in all directions, I gave up. What was going on? (Espeically the road closures.) (I'd like to avoid making this mistake in the future. I know downtown traffic is often bad, but usually not Sunday at 10pm -- even on a holiday weekend!)