When dafont.com says a font is "Free for personal use", could it be used for local student run show posters as long as I'm not selling the posters?
'Free for personal use' means that it can't be used for any commercial purpose. This means that you would be OK to use it for posters that were just for your own amusement or for your own wedding invitations, for instance. However, you can't use those fonts for making money. This would include making posters for a profit making event or for designing somebody else's wedding invitations that you are charging them for.
Your specific case is somewhat borderline. If you are charging the organisers of the run for your poster design then NO, you can't use that font. If somebody (even a charity) is making money from the run (i.e. via sponsorship) then the answer is still probably NO.
However, if you're designing the posters for free and there is no money being made (or even if the only beneficiary will be a charity) then the safest course of action is to contact the designer of the font and ask them if they are cool with you using their font for that purpose. They have the right to say you can't use it or they may want a fee to allow this use and/or a credit somewhere on the poster.