I have used Fuji Natura a few times and can work with it's grain easily. Color and contrast is on the low side similar to the Kodak Portra but of course this greatly depends on how you will get the image from the film.
Full res ->
http://www.fototime.com/44755C7C15E364F/orig.jpg
However, if it is a sunny day with not much shade/shadows, maybe you don't need all that speed particularly since Fuji Natura is not readily available. The shot below is using Fuji Provia 400 - sunny Las Vegas day, and I was achieving 1/8000 shutter speed on my Canon EOS3 and managed to catch the ball in flight.
BTW, I have found Fuji Natura to be slightly less grainy then either Fuji Press 1600 and Superia 1600,