What did I most likely brake on my riding lawnmower after running over tarp? The starter will spin, but the motor does not seem to move and will not try to start? I clear tarp from mower blades.

I'll bet there are tarp threads (most tarps are plastic over plastic weave) wrapped all around all the spinning parts. Did you look really closely, taking the deck off or turning it over?

The starter will spin, but the motor does not seem to move
If that is true, the starter must be geared to the fly wheel.

If starter engages the fly wheel but the motor does not turn during cranking, you have sheared the key between the fly wheel and the motor shaft.

Hi,
If the starter spins but does not engage, I would say you hed the battery out and it is now hooked up backwards.
Peace,
Clarke