Lacrosse is a sport where other than posed shots, the protective gear is going to prevent clean eye detection in most situations so eye detect is not useful. It is also one of the fastest moving sports with a lot of very fast action changes so I would go with single point with four point expansion AF with the selected part of the array around typical chest height. Use AF servo and I believe that AF Case IV is the most appropriate but depending upon your shooting location you may find Case II useful if you have interfering subjects frequently crossing your field of view.
You should be shooting at a high enough shutter speed that image stabilization isn't needed so make sure that you don't have the lens stabilizer turned on, especially if you aren't using the LP-E6P version which maintains system voltage better under high current drain compared to the LP-E6NH. As system current demand increases, a drop in system voltage reduces AF performance. The slowdown with EF lenses is primarily based upon the response of the aperture assembly in the lens which needs to be able to step value with every frame.
To me, Lacrosse is the most difficult field sport to shoot however my camera setup (2 1DX III bodies with EF 400 and EF 70-200 f2.8 lens with aperture set wide open, manual exposure with auto ISO, typically AF case 4 normally single point AF with four point expansion) is the same that I use for soccer and football. I have never been a fan of splitting the AF and release buttons since I always shoot sports with two bodies and sometimes three and often switch bodies during a single action sequence so the less places I have to worry about exact finger placement, the better.
I do make use of the handy array of AF stop buttons on my 200-400 1.4X and great white primes and I have the AF button on the back of the camera programmed for AF stop for those rare occasions when I want to freeze AF.
Rodger
The answer is simple: the Canon R6 Mark II is garbage. They deliberately downgraded the functionality and autofocus performance of this camera.
For six months, I carried both cameras to my shoots (the R6 and the R6 Mark II). I photographed sports, basketball, marathons, red carpets, corporate events, children, and animals. In every scenario except still photography, the Canon R6 focuses better, more accurately, and produces 5–6 times (!!!!) fewer missed-focus shots.
Where I get around 10% failures with the R6, the R6 Mark II gives me 50–60% failed shots in a burst.
A typical situation: a sudden “unique” moment happens. You quickly raise the camera and fully press the shutter button. The burst starts.
With the R6: the first frame may miss, but every single frame after that is perfectly focused. Every single one. No failures at all.
With the R6 Mark II: the first frame misses, the second one hits, the third jumps to another area at the edge of the frame, the fifth and sixth miss again while trying to reacquire the main subject. In the end, out of a 20-frame burst, only about 2 shots are usable, while with the Canon R6 I get around 18 out of 20 sharp images, correctly focused on the original subject.
I will attach some of my work so you can understand my level of photography and the type of situations I shoot.
The only solution is to throw away the Canon R6 Mark II and keep using the R6. It is many times better.
The second option is to disable the tracking autofocus features and use the Canon R6 Mark II like an “improved” DSLR. In my opinion, that completely defeats the purpose.
What frustrates me even more is that everyone is trying to solve this problem through settings and configuration changes, while I strongly suspect that this limitation was intentionally created by Canon for marketing reasons. This is not something that can be fixed by changing autofocus settings.
