This is lens flare from bright stage lights. Strong, focused lights can reflect internally between lens elements and create irregular arcs, blobs, or streaks instead of neat rays. Different lenses flare differently, so the exact shape is normal for that lens/light angle combination.

To reduce it:

• Avoid aiming directly at bright lights when possible.
• Use a lens hood, especially to block light just outside the frame.
• Remove any unnecessary protective/UV filter indoors or at night unless it’s a good multi-coated one, since extra glass adds more reflective surfaces.
• If possible, stop down a bit or use a lens with better flare control.

Some of the blue lines may also be related optical artifacts, and chromatic aberration can make flare look worse.

In concert photography, though, some flare is often unavoidable because the lights are intense and directional. Sometimes the best approach is to change your shooting angle—or embrace it as a creative effect.