One method I like to use is to copy the portion of the element (in this case the sword) onto a new layer. Go to FILTER/BLUR/MotionBlur. Use the directional 'wheel' to determine direction (motion) of blur. Use the bottom slider to set how much blur you want on the element. Move the finished layer below the element (sword) layer, and offset to show desired motion. Use the blurred object's layer OPACITY setting to fine tune transparency. Hope this helps!