I've now shot 6 of my son's soccer matches this season with the new Sony A7 III. This could be a bit premature to be giving thoughts on shooting soccer with the new gear as my longest lens is currently a 135mm, which is in no way a good option for soccer. However, I feel I've shot enough at this point with the A7 III (and comparing it to what I was on previously) to know that this camera can absolutely hang with any modern camera for shooting sports or action.
My History Shooting Soccer
My main camera / lens combination for shooting soccer the last few years has been either a couple Nikon D750's and more recently a D500 as well. I used two lenses predominantly: The Nikon 70-300MM f4.5 - 6.3 VR (not the new ED version) and the Sigma 150-600MM f5-6.3 Contemporary.
The Nikon 70-300MM was my starter lens and did an OK job. Autofocus on the D750 was snappy enough as was tracking. Image quality, in my opinion, was good enough but overall sub-par. Lastly, 300MM is probably the minimum you want for covering the larger size fields.
The Sigma was a pretty awesome upgrade in capability. Image quality, while not perfect, was a nice jump from the Nikon. On the D750 and even more so on the D500, the autofocus was nearly infallible. The weight is a bit much but it's possible to handhold it with good technique.
Autofocus with the recent Nikon gear (D750 and up) is a satisfying and consistent experience. I typically would set a group AF zone and move the zone to my desired composition. This was effective and relatively fast. In more difficult situations, or when I wanted a bit more control, I would just set it to a point and track.
How the A7 III Changes the Game
From the lens perspective (only 135MM), things are obviously not quite there and I'm not shooting as seriously at the moment due to this. I plan to eventually grab the Sony 100-400MM GM but until then I'll take what I can get.
The A7 III's autofocus capabilities are truly awesome. Coming from the Nikons, I now have increased tracking performance as well as additional options to utilize. Face and Eye tracking works very well here (more so with face tracking but with the longer lens the eye could come into play more). Add to this 10FPS (with blackout; 8FPS with viewfinder updates) and you have a serious action contender.
A Few Quick Thoughts on the Zeiss Batis 135MM 2.8
Shooting soccer with a 135MM lens forces you to really pick your spots. You have to anticipate a more and sometimes just get lucky as there is just no way to cover even a third of the field. However you CAN take advantage of close opportunities very well and with a potentially interesting look. The Zeiss Batis 135MM 2.8 lens is extremely sharp, focuses AND tracks well enough for this task and has impeccable image quality. It's a lens that I feel isn't getting the praise it deserves due to it's 2.8 max aperture. Sure, F2 would be great but with that would likely make it much larger to keep it's image quality at this level. This is a gem of a lens and I love having it in my bag.
Zeiss Batis 135MM Autofocus
Not going to get too in-depth here but I wanted to give a quick overview on what settings I choose. Keep in mind the 135MM lens does influence the settings I choose as, most of the time, the action is just a bit further away than I'd like.
I want to be as flexible here as possible. Most of the time the subjects are further away than I'd like so keeping the focus point to it's smallest size is necessary. Once the action gets closure I will, if possible, switch to a wide zone. You start to learn how this camera behaves and how you can influence what it is focusing on in these zone setups. If I don't have time to switch the focus mode then I will keep the point somewhere near the center area and utilize face and eye tracking as the action quickly starts filling up the frame. Again, practice is necessary but my hit rate is unbelievably high. I have more confidence with this setup than I've ever had in these conditions before.