Only when I have to, and since they traded the broken "good" office camera for a point-n-shoot with no manual focus, I refuse to shoot sports.
As far as your pics above, they're all right to begin with, but one thing I learned when shooting and placing photos is this (don't ever forget it): "Real people doing real things."
Otherwise, shoot the "standing still" shots to have something to fall back on, but begin to challenge yourself. One thing I do/did, in shooting baseball or softball, for instance, is focus the camera on a base and then shoot like hell as a runner is moving to that base. Shooting the pitcher is another easy one, because they don't move from your frame much, so you can manual focus on the mound/circle (Please, DO NOT EVER CALL IT A MOUND IN SOFTBALL).
Football, volleyball and basketball? I leave those to the pros. Volleyball is doable, just focus the camera on the setter or server and hope for the best.