Happened to me once. Sitting at a roundabout, car in front moved off, I looked to my to my right and road was clear, moved off and then I heard a bang. The car in front had stalled...the driver leapt out out and I feared the worst but he actually apologised to me for stalling . Other than a cracked indicator glass, no damage, his car was an old MG Magnette, built like a tank. My dad had something very similar. Car in front stamped on his brakes in the middle of nowhere, he'd spotted someone he knew apparently. My dad did an emergency stop and breathed a sigh of relief as he missed the car by stopping a couple of feet away. Sadly , the third car in line hit the back of my dads car and shunted it into the car in front . Quite a lot of damage and my dad was rather unfairly prosecuted for careless driving , as were the other 2 drivers.
Pete