Road racing is relatively free of rules. Either way, explanations govern competition, records and guidelines. Starting blocks aren't allowed at distances above 400 meters. Two false starts disqualify a runner in national and international meets, only one in US high schools and colleges. The starting gun is fired when runners are set, not after a certain time following the set command.
Sprinters are usually the only runners anxious about start rules.
It isn't necessary to completely cross the finish line, only reach it. Place is decided by when the torso reaches the finish and the torso is not the head, neck, arms or legs. The finish line is at the inner edge of the line and runners start behind the start line. The torso rule is why you see people diving forward at the finish. There are four barriers and a water jump on each lap of the steeplechase.