This question depends on the person. Usually by around 200 to 210, your heart begins to go into an abnormal rhythm or disrythmia, called VT or PVT. The respectively, stand for Ventricular Tachycardia and Pulseless Ventricular Tachycardia (PVT is the more dangerous variety). At around this stage a patient runs the risk of cardiac arrest, which is dangerous because while the heart continues to beat, the contractions are so fast, blood isn't being let into the chambers of the heart. Without blood actually being pumped, the person is unable to perfuse, and goes into shock, seizure, coma, and then death.
B...............................
It's important to take your time in any game that requires focus, strategy, and quick thinking - while you have to be in physical shape for baseball, you also have to have the mental capacity to be aware of every thing around you and look for the perfect opportunity to make any move so that you can make the best possible move.
Examples: (Hitting the ball at the perfect time with the right amount of force, knowing when it's safe to run home or if you need to stop at what ever base, being aware of where the ball is at all times, knowing where/who to throw the ball to when you want to get someone out, knowing how to pitch the ball to trick the batter.)
