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
