Hail is frozen precipitation that can fall during a thunderstorm.
Typically you'll find hailstones that arrive to the ground showing up no larger than a quarter of an inch in diameter. Sometimes, however, they can be a bit larger. So large, in fact, that your poor car is going to take a serious beating if it's out during such a hailstorm. This is what a bunch of folks in Colorado experienced as their vehicles were pelted with hailstones the size of golf balls dropping from the sky.
The dashcam video shows a car on Colorado's Interstate 70. Large bangs are soon followed by the cracking of the front windshield. That's all followed by swear words, which we can all agree are pretty warranted here.
There's nothing you can do in this case. You're out in traffic on the highway, and you're all experiencing the same thing. If you're fortunate enough to find an overpass, make sure to pull over until the storm passes. Otherwise, you'd better hope your insurance covers any of the damage your car or truck is currently receiving. Body panels will be dented and windows will be cracked and broken.
It won't be fun, but it's better than getting hit on the head by one of these hailstones.