Who uses a grey card in Arena settings?

Just curious how many sports photographers will shoot a grey card

before an event at an arena? I have only seen one photographer do it.

Recently photographed a gymnastics event and found the color was

variable depending on the event.

 

See examples from the

event:http://www.gymnasticsrevolution.com/Parents%2024.html

I have not tried setting the white balance with a grey card before but after reading up some yesterday will try it on my next event where I'm shooting inside a gym or arena. Shooting Basketball events for high schools I sometimes have found that I have problems and this may be the solution.