Abstract: An indoor sports arena of the type having a massive floor structure, e.g. for tennis, track and other athletic events requiring a cushioned tread by the player or sportsman, comprises a resilient underlayment of open work structure which can be bonded to the surface and is underlain by a packed particulate material usually of a sand, red sand, cinders or another composition commonly used for outdoor track and sport fields. The open work can consist of a nonwoven mat of fibers, a screen, or other cellular open work layer of natural or synthetic fibers which can be bonded by an elastic adhesive to the underlying surface. Excellent results are obtained with an underlayment of coconut fiber.