Went through a car window

Register - you know that if you're behind someone and they get outbraked by someone driving like a dick in front of them causing you to hit them from behind it's still on you right? What caused the car to come to a sudden halt in front of you is totally irrelevant no matter what. You have to be prepared enough and far enough behind someone to stop in time if they have to pull up quickly or if they hit something. End of. So don't blur the argument with the car in front who drove away. You did the right thing stopping and swapping with the driver. The rest of this argument isn't standing you up in such a good light.

How about if the car is in the wrong lane? I was in the middle of 3 lanes, left and middle going straight and right turning right. At green the car in front started moving and I sped up and then suddenly car braked and indicated right and stopped as it waited for a car to give it way. I swerved but still hit the left side of the bumper and fell off to the side.

Whose fault here?