Thank you all. I really like sports photography, and try to bring out the human side.
Dallas and Mike, the answer to the gear question is a bit complicated. Fixation (where I rented the 200-400 for Sabi Sabi 2010 (Ann, I think the Wimberley impressed you)), had an offer over the Easter public holiday - four days rental for the price of one day. So I rented the 300 2.8, a £4,600 lens for £45, and a D500 for £50 for the same period. These seemed to be unmissable bargains.
On the day, I had the above rented items, plus my D3s (a veteran of Sabi Sabi 2010), the Nikon 70-200 2.8 and the X-T2 with the 50-140 and 18-55 (used for the view from above). Mostly I used the D500, because I wanted to give it a thorough check out. In the morning I used it with the 300, with the 70-200 on the D3s, in the afternoon I swapped them round. I used the X-T2 with the 50-140 as well, because I wanted to test it out in the challenging circumstances.
My first pass on the results showed that each combination was very capable of tracking the action. However, overall the D500 came out as the winner. But the other two cameras were not far behind. The 300mm was a bit too powerful, as I was able to get fairly close to the action. But it is a wonderful lens. The photos in the post were all D500 apart from two which were X-T2; I do not put too much weight on that, as so much depends on external events, e.g. whether a competitor had an arm covering the face in what would otherwise be a great shot.
My conclusion is that Nikon has the best overall system for this type of shooting, with the D500 outstanding. But the Fuji combination performed very creditably, and I do not feel the need to acquire a D500. However, Fuji's lens offering for sports photography is too limited. So I may well rent the same combination again.
Dallas and Rags, the spray does indeed make tracking focus tricky. I set all the cameras to ignore distractions to the maximum extent. Inevitably there were many failures. I tried the D500's 3D tracking with Face Recognition; the focus box jumped around the frame in an alarming manner, but on reviewing the results on the computer, it actually had quite a good hit rate. The Fuji was much better for reviewing on site, because of the EVF. The LCD screens on all the cameras were useless for serious evaluation, because of the sunlight.
Ann, you have set me a tough Photoshop exercise!
Chris, actually, it is a young woman!