This rule applies to spectators who are walking around, grooms in the paddock and everyone standing up. People who are seated in their 'bubble' don't need to wear a mouth mask. Riders on the horse don't have to wear a mouth mask either. 

The Belgian Federation asks everyone to follow these measures in orde to still be able to keep on jumping for the rest of the season. "Numbers are bad and we all have to take our responsibility for our sport", they say.