I am having a problem. My x-cellerator will start but the car won't go. When I give full throttle the car we only move slowly. If I hold the car in place on the ground and give it throttle, the spur doesn't turn but I can hear the engine rev up high like normal. It does look like that piece is spinning (flywheel?) that can be seen from underneath the car through that slit in the chasis. The diff is tightened all the way.

It happened after driving it around my backyard off of the porch and through the rough grass.
Could this be a problem with the clutch?