When shooting crowded events or tightly packed performers, it’s all the more important to isolate your subjects by throwing the background out of focus.
When shooting with primes, remember to use wide apertures. Wide apertures = shallow depth of field = more background blur.
When shooting with zooms use wide apertures and remember to zoom in as far as you can without excluding the important elements. Shooting at longer focal lengths = shallow depth of field = more background blur.
If more depth of field is needed shoot at wide angles with smaller apertures.