Holy balls! Did you watch the Home Run derby the other night? I didn't. But if I did, I would have wondered about the same thing: How did they manage to show those cool balls' trails in real time?
The mechanism involves a complicated mathematic algorithm that tracks and predicts the ball's trajectory in real time, only 400 milliseconds after being hit. To get the data needed for the calculation, ESPN uses a 2000Hz Doppler radar which follows the ball's speed, location and spin, giving precise data of distance travelled - something that before took precious seconds or even minutes to calculate. The path is calculated and shown overlaid on screen in real time, precisely chasing the ball.
The results are quite cool, even though they fail (again) to make baseball exciting to anyone outside the US. [Popular Science]
And yes, I hereby declare today Gizmodo's Official Ball Celebration Day.