Once, Marc Rosenberg was just like any other lemonade vendor prowling the upper decks. He hustled, though, and was promoted to the third-base side lower boxes. Then, on a humid 98-degree Baltimore day, with every kid in his section screaming for a lemonade, the inspiration came.

“I put the tray down”, Rosenberg remembers, and I started flipping out.

Now, Marc Rosenberg, 34, is the Lemonade-Shaking guy. His sktick is a Jumbotron staple-a frenzied seizure of a dance routine that accompanies every freshly shaken lemonade he serves. (Well, almost every one: About five percent of his customers, Rosenberg says, “don’t want the shaking.”) Rosenberg works the crowd tirelessly, exhorting kids to jump up and convulse around in the aisle with him. “I want to make it like a party every night,” he says.

He’ll lose about five to six pounds per game on a warm night. It’s a small price to pay for his new slot on the prime first-base side. But Rosenberg knows that he needs to keep the routine fresh; this season he promises several innovations. “I got fake teeth, I got wigs, I got funky glasses,” he says. “I’m going for shock value.”