(The trial court prejudicially erred in excluding plaintiff’s expert’s testimony. Plaintiff was a train worker who broke his leg on a fall from a train. The expert had been an engineer for the same railroad for many years and would have testified that the engineer on the train from which plaintiff was injured released the brake before hitting the accelerator, causing a sudden jerk as the expandable space between train cars suddenly was collapsed. The expert had relevant experience with which to form the opinion which was relevant to showing why the railroad was negligent and why that negligence caused the plaintiff’s fall and injury.)