In Florida, there is a presumption in the law that the car from behind is at fault; however, that presumption can be rebutted.
First, it is possible that the car in the front backs into the car from behind, causing the accident. If those are the facts, then the car in front is at fault.
Second, there are some common scenarios that may lead to fault on the car in front. If that car suddenly stops, then it may bear some fault. Further, if the car suddenly switches into the lane and then is hit from behind, again a jury may find that car in front to bear some fault.
As discussed in other posts, Florida is a pure comparative fault state. Thus, a jury can apportion fault (80 percent/20 percent, 70 percent/30 percent, etc.) between the parties. However, in the most common rear end collision where one car is stopped (at a light, for example) and another car crashes into it from behind, that scenario generally there is 100 percent fault on the car from behind.