Stage LIGHTING can often be quite intense and bright! You can easily be fooled, if you are sitting in the dark, and the stage and its people are all lighted. The single BIGGEST PROBLEM with shooting things that are up on a lighted stage is OVER-exposure caused by a meter that "sees" a large expanse of dark curtains, or dark set. Red velvet drapes, blue velvet drapes, black velvet drapes, black-painted stage walls, all of those things can easily be eight to 10 f/stops darker than somebody who is 15 feet in front of the curtain, and happens to be lighted by a spot or strong floodlight.
"Many" cameras will tend to over-expose the actors/pitchmen/speakers when the lens is set to wider-angle views; the speakers/actors might be 5% of the total picture area, and if the background is 90% dark,well, you can get some MASSIVE burn-out on people. With a longer, more-telephoto lens, light meter readings that do not include so doggone much dark background--are usually more-reliable meter readings.
If you ARE in an AUTO mode, and shooting with a short, wide-angle lens you might have to dial in Minus Exposure Compensation, as much as 3 stops, or more--if the STAGE and background are really dark, and the people are lighted up really brightly.
If you are shooting telephoto shots...you ought to be able to get more or less accurate readings using center-weighted, or semi-spot readings. If the lighting is the same for the whole show, you can arrive at the "right" exposure one time, using either exposure comp in an auto mode, or manual metering in spot, or trial-and-error, and then just shoot at the same exposure value for the whole show.
If the lighting is gonna Yo-Yo like,well, a Yo-Yo, with multi-colored spots and floods and scene changes constantly...you might really consider going to AUTO ISO mode, center-weighted metering, picking a HIGH maximum, like 3,200 ISO, and a shutter speed that is likely to be motion-stopping and lens-shake stopping, like say 1/100 second, and then letting the camera's AUTO ISO keep you adjusted as the lights swing back and forth.