aerobic means you are using your lungs and cardiovascular system.so, when you stop working hard using your lungs and cardiovascular system, it becomes anaerobic exercise.Running, swimming, etc =...
Baseball is both. It is an aerobic exercise because you are moving constantly while you are running bases or in the outfield. If you are bating, you use short bursts of energy to hit the ball and run...
Aerobic (meaning with air) exercise primarily works your cardio vascular system, like aerobics, biking or running. Anerobic (without air) is like weightlifting