"The athletes are running back from the place, from where the buses start."
Translation:A sportoló onnan fut vissza, ahonnan a buszok indulnak.
Is this sentence OK: "A sportoló onnan visszafut, ahonnan indulnak a buszok." (I know "sportolók" will be rejected so I used the singular, but I thought my translation had internal logic at least.)
It doesn't seem to like "visszafut" but I don't know why. And I don't know why it doesn't like the order I used for the last 3 words.
Yes, otherwise the preverb/prefix would "steal" the emphasis from "onnan", the word you actually want to emphasize.
There would be a special emphasizing where there is an "onnan ... ahonnan" yet the verb is not split up. But it has a different meaning. Instead of "that specific place", it would rather mean "such a place". But it would be more natural if the word order were also changed, switching "onnan" and the verb. Here is a simpler example:
"Onnan megyek ki, ahol nem szolgálnak fel sört."
Which place am I leaving? I am leaving the place where they do not serve beer.
"Kimegyek onnan, ahol nem szolgálnak fel sört."
What kind of place do I leave? I leave (any) such place where they do not serve beer. Emphasis on the verb "kimegyek". It could also be said with this order:
"Onnan kimegyek, ahol nem szolgálnak fel sört.". But this is less natural. And the emphasis is invariably on the intact verb, not on the word "onnan" in front of it.
Other than this, the last three-four words should be accepted either way: "ahonnan a buszok indulnak" or "ahonnan indulnak a buszok".