An employee was unloading bundles of rebar from a flatbed trailer and rigging them for a crane lift using wire rope slings. He was holding up the rigging until the slings began to tension and was positioned alongside the load. As the crane operator began to tension the load, the boom deflected, resulting in the boom tip sheave traveling laterally and losing alignment with the center point of the load. The resulting angle of the main hoist line caused the load itself to move laterally once it was up off of the trailer. The employee had to secure himself to the load to avoid being knocked from the trailer. The signal person who witnessed the event directed the crane to lower the load. While the load was coming down, the employee attempted to regain footing on the trailer and ended up with his left foot below the load. The load contacted his lower left leg, fracturing his tibia and fibula.