EE was flagging the crane operator while the forklift was being used to pull the crane into gear. The crane went into gear. A 3"" nylon strap was hooked up to the crane and a 3/8"" choker was hooked up to the forklift. The strap and choker were connected with a 7/8"" shackle. Due to too much tension the choker broke. A slingshot effect occurred and the shackle hit employee's leg.