Paintball competitions have regulations just like other sports. Paintball balls have to be a certain size and can not be pink or red.
9.01 Specifications. In accordance with marker requirements, paintballs must be .68 or .50 caliber. Paintballs used at any NPPL tournament must be purchased onsite from the League or a sponsor paintball manufacturer that has certified compliance with ASTM standards and meets NPPL non-staining criteria available on the official NPPL website www.nppl.com Players may not bring any paintballs onto the site which are not supplied from within the Players Paddocks. See Exhibits ASTM Standard F1979-04. Paintballs not supplied on site by approved onsite NPPL vendors is considered Prohibited Paint. See Rule 18.01 (5)
9.02 Pink and Red Paint Prohibited. Players may not use pink or red filled paint (“Prohibited Paint”). Players using Prohibited Paint or paintballs that do not comply with ASTM standard F1979-04 or NPPL non-staining criteria will do so at their own risk and will be subject to penalties in Rule 18.01(5), including assumption of full responsibility for any resulting injury or property damage.
National Professional Paintball League Rulebook – http://nppl.com/wp-content/uploads/2013/03/NPPLRulebook2012.pdf
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