Here's a scenario: You're running down an ATV trail that has two equally preferable running paths. You happen to be on the left path. There are no runners anywhere ahead that are near. And except for the approaching footsteps of the runner who is behind you, there is no one else there either. As the footsteps get really close you hear the familiar words, "On your left!"
Now, most of the time, common courtesy for slower runners is to let faster runners pass on the left. It's just what's done. But here is an interesting situation. You have to alter your run to cross from the left lane to the right to allow a runner, who had plenty of time and ample opportunity to get to the right for a clean pass, to pass you by.
What is the right thing to do?
As I've participated in OCR for a few years now, I've noticed that not everyone who participates in the sport are lifelong athletes. A significant number of people are relatively new to any athletic endeavors and as a result, aren't necessarily aware of some of the rules that have been handed down from early days of track and field or cross country. And even some who used to participate in the running sports "back in the day" have forgotten (or never really learned) a some of the basic rules that many race officials would tell and retell at the starting line.
The main thing to never do in competition is to interfere with another athlete. Even if it means you have to adjust what you're doing. In running events, you need to be at least a stride and a half ahead of the person you're passing before you can cut in front of them. This way, you don't get your legs tangled with theirs or cause them to interrupt their stride.
It also means that the person in front of you has no obligation to move so you can pass. That's right, they aren't required to move. It is up to the passing runner to get by without interfering. (Now, if the front runner intentionally gets in the way of a passing runner, that's illegal, so don't do it!)
Of course, in the sport of OCR we're taught to allow runners to pass "on the left". But this is a courtesy, one that should be afforded to faster runners whenever possible. This does not mean that the slower runners up front absolutely have to get out of the way right this instant, I don't care if there's a sheer cliff to their immediate right and a vertical rock wall to their immediate left, I'm faster and I need to pass 2 seconds ago! Courtesy goes both ways.
So, that scenario from the beginning. How should it be handled?
If the runner in the front hears the approaching runner soon enough, they can slide to the right as soon as they can (being careful not to cut the approaching runner off in the process) so that they can pass safely and easily.
Also, if the front runner doesn't move (maybe they don't hear the footsteps, maybe they're just "in the zone", maybe they really like the soft moss in the left lane over the short grass in the right) then the approaching runner should move to the right lane when they can and pass the slower runner without fuss.