General note: had I had the time to actually post this right after what I'm about to tell you occurred, the title of this post would have been "Waterfalls are evil" and my tone would be much, much more abrasive than what you are about to read. Alas...
In athletics, all sprint and hurdle events, which include the 60, 100, 200 and 400 metres and the 110 metre and 400 metre hurdles for those unfamiliar, are started in lanes, and competitors stay in the same lanes throughout. Whenever the race is not in a straight-line, which includes the 200, 400 metres and 400 metre hurdles, the starting positions are staggered (separate lines with lane numbers) to ensure that everyone runs the same distance.
If started in that way, competitors will immediately push for the inside, causing some competitors to be either boxed in or boxed out, with some elbowing along the way. Unlike distance races where competitors have time to move out of their confines for the inside before the finish, the chances of a 400 competitor moving up out of their boxed-in position without running the risk of disqualification is very, very low.
Furthermore, at the start, the standing start must be employed, not the block or down start. This practice favours distance runners who never start down in the first place and consequently disadvantages sprinters because they mostly, if not all of the time, start down. As the 400 metres is a sprinting event, more harm is done to sprinters because the standing start is simply not in the sprinters' training programme.