blah blah, yes you can always find pictures like that on the internet. if its not detectable to the naked eye (and often, when a racewalker is going fast, they are on the "edge" in terms of legality anyhow) - its legal. You can say it sounds stupid all you want, but I'm sure there are plenty of throwers who fouled and an official missed it. It happens.
And the OP made it sound as if someone broke into an actual SPRINT - which another poster was correct in saying was probably BS. There are officials set up at the end that will toss you if you're too flagrant in the last 50.