Small Engines (Lawn Mowers, etc.): cant get riding lawnmower to turn over, riding lawnmower, fly wheel

Question
what would cause the fly wheel to get stuck and not turn easily to start. Thought it was a weak battery but that is not the problem. I sometimes can give it a push with my hand helping it to spin a little but that isnt working now either.
It is a briggs and straton engine for a yard machine riding lawnmower.

Answer
Will the starter turn engine with the spark plug removed?  Does the oil smell like gasoline?

Dirty battery connections?  I have fixed many, many starting problems just by dis-connecting the battery cables and cleaning the battery terminals and cable ends with a wirebrush.

How old is the battery?

Let me know.
Eric