Sorry I'm so late to answer your question. The 3rd base coach has more than one thing to relay to the runner coming in as well as any other runner approaching 2nd. Unfortunately, he only has 2 hands. Generally, if the runner needs to slide, he will be using both hands to indicate a slide and to which side of the bag. If a slide is not necessary, the left hand will be raised to indicate a stop at third with or without rounding the bag. The right hand will be pointing to where the ball is or where it is heading. If there is a second runner heading toward second, often the coach will be looking at that runner to insure he is catching the signals he is giving. So, as you can see the 3rd base coach has multiple duties all at the same time. Hope this helped.