I grew up in Pennsylvania and this incident happened to me and my family. One day, as the rest of the family was outside and my friend was in the bathroom or something, I had wandered into one of the many big rooms in the house.
I gazed out of a large window, to the big pine trees, when all of sudden an ENORMOUS bird/bat-like creature swooped low in the canopy and then veered out of sight. I couldn't believe what I just saw! In the few seconds that I got to study it, I noted it was a dark brown in color and had a huge wingspan, but the wings themselves looked very bat-like, as if skin was stretched between feathers (or bone?). And its head was huge... as big as one of their shaggy dog's heads! But it had bright yellow talons curled beneath its body.
So it had to of been a hawk of some sort right? I don't know exactly... but I know what I saw! Later that same day, I told my parents what I saw and they laughed it off, only to become believers themselves.
As we were taking our leave and driving away from the farm on their winding dirt driveway, something huge and brown crashed directly into the passenger-side window where my mom was sitting! She, my brother and I all shrieked and my dad stomped on the brakes. We only caught one more glimpse of it, though, as it hopped and rolled as if wounded on the ground and then jumped into the brush, out of sight.
It resembled a large, feathery, brown rat. I remember grinning and exclaiming, "You believe me now?!"
"Yeessss!" everyone else cried in unison.
"What the heck WAS that thing?" screamed my mother.
"It was just a big bird. An eagle perhaps," insisted my father.
My brother and I shook our heads. "It looked like a giant bat with feathers!" said my brother. We gauged the creature's body to be about three and a half feet in width and the wingspan of maybe 15 feet. It was HUGE. I've never seen anything like it and have never seen it since.
This was maybe in the late 1980s, so we didn't have internet access, but we tried looking through our various encyclopedias, to no avail. My dad will still bring it up from time to time, whenever the current conversation turns toward the bizarre or unusual, so I know this wasn't some delusion from an over-active childhood imagination.