I LOVE the park runs, me. I've actually won seven outright and still own a few age records. But I never mention that!
The saddest thing I saw (prior to March last year of course) was a woman who turned up at my local one New Years Day. We always do that one at 10.30 to allow people to do a nearby one at 9.00 to start the year on a double and get three in a week. She'd turned up because the year that ended the day before had seen her and her husband attempt to do 52 different courses in that year (2018) and all had been going extremely well...until they were on their 50th. Her husband fell awkwardly on an icy patch and he went down ripping his ankle ligaments. His attempt was sadly over but she stayed with him, providing assistance and eventually helping him back to their car but by the time she got to the finish line, they'd all gone so her time couldn't be recorded. So close and so cruelly snatched away from her on her 50th run!
But we have a club house our runners use and it's usually the highlight of my week with all the happiness and endorphins blasting out, catching everyone in its wave of pleasure, relief, talk of progress/setbacks/awful-good conditions. Can't come back soon enough for me.