What would cause a riding mower to stop running while cutting?

There could be a million things... what did it do when it stopped? What does it do now when you try to start it? Does it have gas? Sorry wasnt being rude, just asking.. Have you checked the belts? It could be that the load you are putting on the engine is more than it can handle. Also, sometimes the vibration of the engine will cause the carburetor needle valve to rotate one way or the other. Try opening the needle valve (rotate counter-clockwise) about 1/8 turn for a slightly richer mixture.