Complex sentence: Although it is still permissible to play on natural turf (grass) all national competitions and international matches must be played on an artificial surface; currently elite-level competitions, such as the Olympic Games and World Cup, require a water-based playing surface.
Split into simpler sentences: Although it is still permissible to play on natural turf all national competitions and international matches must be played on an artificial surface. Elite-level competitions, such as the Olympic Games and World Cup, require a water-based playing surface.