How does a runner know when to start in a relay race?

Answer 1

Most runners put a piece of tape or something similar on the track (I once saw a provincial medalist use some nearby dandelion from the infield when I was the exchange judge on one corner). When their teammate hits this mark, they turn and go. In general, the faster the runners, the further away this mark will be. Most high school runners need between 15-20 foot lengths, though the speed difference between the runners plays an important part.

You might need only 12 steps if you're a fair bit faster than the incoming runner, but 20 if you're a fair bit slower. It's a reliable way to count (using whatever shoes you'll be racing in), because you'll always have the measuring device handy. In practice, the runners find out how many steps they need, then use that come race time.