Like a modern-day presidential candidate, WETA-FM classical deejay Nicole Lacroix spoke in a vast stadium Sept. 13, though the crowd had not really come for her. The spectators had come for Washington National Opera’s opening night free telecast of La Traviata to the Jumbotron at the city’s new baseball park. Lacroix was “charming and knowledgeable” as emcee, according to critic Micaele Sparacino on Concertonet.com, an international website that covers classical music. He noted that the audience was full of 20-somethings, some with their kids. A press report said the opera filled about 15,000 seats, just over one-third of the stadium’s capacity. Lacroix, weekday evening host on WETA, has been an almost too wonderful presence on WETA for 10 years.