Hello I've shot youth soccer for years with amateur level equipment but have wanted the quality of my photos to look more professional so upgraded my camera body and lens to a Canon 1DX and Canon EF 400mm f/2.8 IS USM lens (older ver. lens not the new one). I have a lot of blurry photos and most of them are not very sharp either. I am not sure how to correct the problem since I am new to this camera body. I read up on the case settings and recommendations quite a bit before the shoot but not sure how to correct the problem? I shot in Case 4, Tracking Sensitivity -1, Accel/decel. tracking 1, Af auto pt switching o. 8 point expanded center pt AF selection. AI Servo Continuous H. Using back AF button not shutter button for focusing. Image stabilizer was turned off on the lens. 10m-infinity setting. The lens seemed consistently slow to autofocus especially the further I got toward the other end of the field. I've tried increasing the Case parameters to +2 for emphasis on faster focus speed but with no better results. Any help would be greatly appreciated.