Here's a small taste of what Preakness used to be with BYOB:
Something had to be done to reign it in. The infield didn't even resemble anything close to a horse racing event. It was just 100,000 college kids getting trashed and causing mayhem.
In my early days working for tote, I got tasked with helping pull terminals out of the infield the day after Preakness, and the place looked like a damn landfill. I saw people leaving behind couches, swimming pools, kegs, clothing, and enough empty beer cans to build a new grandstand. You could barely even see grass, and that's not an exaggeration.
When Pimlico banned BYOB starting in 2009, there was a temporary dip in attendance, but it's come back pretty strong since then. It's still a party in there, and there's still plenty of alcohol to be had; you can buy beer mugs with free unlimited refills for $20 (or it may even be free with certain ticket packages). It's just not quite as crazy as it used to be, which imo is a good thing.