Massachusetts uses a “modified comparative negligence” system to allocate fault. This means that you can only recover for injuries if you are considered to be less than 51% at-fault in the accident. In other words, if a judge or jury determines that you are 51% at fault or more for the accident, you'll recover nothing.
The determination of fault is made by the insurance company that makes the claim payment. The standards of fault are established by 211 CMR 74.00 in accordance with Chapter 175, Section 113P of the Massachusetts General Laws.