I would point back to my comment – just because you hit something with a rock doesn’t mean you kill it, especially if that thing is the size of a dog, child, or adult. I know it’s morbid, but I wrote a paper on people being stoned and saw videos of it. You can think what you want, but a human can take a lot of abuse, and a zombie is even more resilient when it comes to blunt impact on most of their person.
Also, as we’ve discussed, throwing a uniform item specifically designed to throwing (a baseball) is not the same as throwing a rock you just grabbed up off the ground or a less aerodynamic object like a stick. But, let’s track that line of thought. People get hit in the face with baseballs. It happens. They walk away with an orbital fracture or broken jaw (Rhys Hoskins). Disoriented, stunned, and injured, sure, but not dead. You hit them 2 or 3 times with a baseball going around 95mph, sure, you’ll kill them, but that’s beyond the scope of the average human. I acknowledge that most of our characters, though, are above average.
Also, a 10 year old kid throwing 90 mph is pretty astonishing and I honestly don’t even believe that. It definitely should not be considered the average.