Many thanks for all your quick replies.
First--Jerry, I have followed your advice and have bought the book you have recommended. So far, I am really enjoying the author's explanations for focusing with the Nikon 750's many options.
Kymarto---Apparently the general consensus of professionals is to use manual focus as you are suggesting. I am reading Richard Harrington's book, "Creating DSLR video, from Snapshots to Great shots", and like you Richard strongly advises shooting manually. Richard claims using a loupe really helps with the manual focusing. With the Nikon D750 I can magnify the image in live view to more precisely set the initial focus but while I"m actually shooting the video I can't magnify what I'm trying to focus on. Richard uses a Zacuto Z-Finder. I'm finding loupes from other manufacturers at amazon.com such as Hoodman. What is your opinion about using Loupes?
Prior to shooting this last fight video, I even experimented in my condo living room with manual focus. I tried to remember what the ring dimensions might be. Then I set my tripod out at various points of my living room and shot experimental short videos using it as a focus point. I then used various f stops in aperture priority so I would get varying depths of fields. Then I'd check the videos to see what points in my living room were in focus and which ones weren't. I thought I might use say an F-8 when I got to the fight and if I set the manual focus to say the midpoint of the ring,that I might get the two fighters in focus either at the far side of the ring or when they were right up on the ropes 15 feet in front of me. But when I actually got to the fight and eyeballed how the distances would work out, I thought..."No way. I am too close to the ring and there's too much of a difference between my camera and the front of the ring compared to the camera and the far side of the ring to make that work out well."
Here's another fight https://www.youtube.com/watch?v=cLrZQ_P7ucA
At 5:44 into this video I suddenly noticed that my buddy, Big Daddy, was going crazy when the double knockdown occurred. I instantly switched from focusing long range to up close and personal and luckily the automatic focus locked right in. I don't think I ever could have managed to manually focus in time. However.......I've oftentimes practiced shooting video down at the beach at an outdoor restaurant we frequent. This is in low light. Here, I'll be in nearly perfect focus shooting distant subjects. But if I want to quickly pan my camera to the people at my table, I will oftentimes lose my focus and the automatic focus does not bring my close by subjects into focus. I will then have to adjust manually. So, you are right, the camera does seem to behave erratically in auto focus.
As to the sound quality. The sound level and acoustics at the Max Pattaya Stadium are almost intolerable. The Thai announcer speaks much louder than he should in my opinion. And the music's playing so loudly that the floor is shaking. It's also distorting to a painful level. This is not coming from my camera's internal microphones. I can lower the decibel level in my video editing program. I am using Cyberlink Powermaster 15. I can easily mute the background sound, and I can also edit it by bringing the Soundtrack into Cyberlink's Wave editor. I am not an expert with the audio by any means, but for example, I can lower the decibel level of the soundtrack, but the distortion is still there, and then the background sound of the fight ends up not being realistic.
No matter how proficient I could ever become, there's no way I can compete with the professionals doing video for the Fight Channel. So what I'm trying to do is to give my viewers the sense of actually being there, in the Max Pattaya Stadium itself. I've found in general that Thais, compared to Europeans and Americans, have a much higher tolerance for pure noise. In a similar U.S. stadium, music would normally not be played at such a high level of distortion. Here it seems very acceptable to a live audience that is over 90 percent Asian most of it Thai and Chinese.
I suppose I'm still hoping that the automatic focusing will work. This in spite of a good buddy's advice to me that the Nikon 750 has a mirror and that it won't work nearly as well as my Panasonic LX7 or the new mirrorless cameras now coming out, especially from Sony. So I will be paying close attention to the book I'm now reading about the huge number of automatic focusing options the Nikon D750 offers. But I keep being reminded that using manual focus is the only real viable way of shooting this type of video with my Nikon D750. I am being reminded not just by other people but also through many many hours of my own experimentation stretching over many weeks.
Another possibility that I've entertaining is upgrading from my Panasonic Lx7 to one of the newer Panasonic models. For example there's the Panasonic LX100. This model is about two years old. The camera only has about 12.5 megapixels resolution to my LX7's 10, but the sensor (a 4 3rds format) is much much larger. It has a normal viewfinder so one is not having to use an LCD screen such as I'm doing with Nikon's live view. There's also the new Panasonic LX10, which has a 20 megapixel resolution and (I think) a larger sensor (1 inch) than my Lx7 is using. For what they are these Panasonic are wonderful little cameras. Both the Lx7 and Lx10 use Leica 1.4 lenses while the Lx100 has a 1.7 Leica lens. My Lx7 is easy to stay on focus shooting video in low light situations. But on a good day my Nikon d750 will blow it away. And as good as they are, they won't begin to replace a good slr like the Nikon D750 doing digital stills.