Looks more like motocross to me
Anyway the pictures:
#1 - Good capture, but looks a bit dark on this monitor. The framing as it is looks a bit tight to me (his foot is really close to the edge of the frame), but the main thing for me as someone who participates in extreme sports is that there is no context, you can't see where he's come from or going, is he 2ft in the air or 20ft?
#2 - Good composition within the frame, lighting looks tricky on this one as the sun is coming from his right and you are shooting his right side, so quite contrasty. My main nitpick would be the chopped off heads at the bottom of the frame, zooming out would have given the context (see #1) or a lower viewpoint would have the rider in the sky without heads.
#3 - I like details shots like these, shows what the event is about (bikes and mud!)
#4 - See #1 & #2, but also there are leaves in the frame that could be cropped out, but the top of his head has been cropped out.
#5 - This one looks a bit soft, but it is my pick of the bunch, you can see where he came from and is going and his eyes which is always a bonus in this type of shot. Maybe the shot could be improved by having more or less tree in the frame, but that would be something to experiment with.
#6 - This one looks a bit dark too, and all my comments are covered on the earlier shots.
