Ever wonder when it's a good time to use the spot meter setting on your camera? One place is whenever you are shooting stage events where the spotlights are your illumination source. The lighting situation is extreme with very bright lights on the singer but the background falls into darkness. Here is an example: With the camera meter set on "Average metering", the light meter averages the scene exposure wise. So the camera, wanting to expose to medium gray, sees only dark clothing and the deep toned background. Thereby overexposing the scene.
Now is the time to switch the mode from average to "spot" metering. This will tell the camera to only make what's in the spot (based on your focus setting) of your camera exposed for medium gray. Simply keep the spot (focus point) over the face (since that is what you are usually focusing on anyway at a concert) and you should be good to go. Remember to turn the meter mode back to "average" metering when you are done so your next images can benefit by the advanced matrix averaging system on your camera.