MOSCOW — The stories about vengeance at the Bolshoi Ballet go back centuries: The rival who hid an alarm clock in the audience, timed to go off during Giselle’s mad scene, or who threw a dead cat onto the stage at curtain in lieu of flowers. There are whispers of needles inserted in costumes, to be discovered in midpirouette, or — the worst — broken glass nestled in the tip of a toeshoe.

But this ballet-loving city awoke on Friday to a special horror. A masked man had flung acid in the face of Sergei Filin, the artistic director of the Bolshoi, causing third-degree burns and severely damaging his eyes. Video from the hospital showed Mr. Filin’s head covered entirely in bandages, with openings for his eyes and mouth, his eyelids grossly swollen.

Though police officials said they were exploring theories including disputes over money, Mr. Filin’s colleagues at the Bolshoi said they suspected professional jealousy. In recent weeks Mr. Filin’s tires had been slashed, his car scratched, his two cellphones disabled, his personal e-mail account hacked and private correspondence published, according to Bolshoi officials. On the day of the acid attack, Mr. Filin had met with the Bolshoi’s general director, Anatoly Iksanov, and confided that he was beginning to worry about his children’s safety.

“Sergei told me that he had the feeling that he was on the front line,” Mr. Iksanov said at a news conference on Friday. “I told him, ‘Sergei, I’ve already been on the front line for the last two years, it is part of our profession, the profession of the leadership, so it’s normal.’ ” Then Mr. Iksanov paused. “No, no, it’s not normal,” he said.