Yeah that's the weird part, that she was able to leave the course and cut off a chunk of it without apparently being noticed.

I would imagine - well, depending on the formality of the event - that there would be frequent 'checkpoints' to log intermediate times and calculate average speed, like once per kilometer or so or even more frequent. If cheating is that big of an issue, of course.

I don't think most races of this type are on tracks. They are on big loops through the city and/or countryside, and the runners do one lap. At most places one might spectate you'll only see the runners come by once, which unless you are a very hardcore fan is not going to be interesting except if you are near the end of the course or if the event is something exceptional enough such as the Olympics that simply seeing any of it live might be interesting.

For an event that seems to be held regularly and seems to be just one of the nearly 3000 half-marathons [1] that happen each year in the US I'd not at all be surprised if there are parts of the course that don't have any spectators.

[1] https://www.statista.com/statistics/280485/number-of-running...

> She cut the course about 3/4 of a mile from the turnaround – cutting a total of 1-1/2 miles.