Sam can be seen wearing a cast on his hand/wrist. Jared Padalecki injured his hand during a stunt in 2.03 Bloodlust (2006) and began filming 2.04 Children Shouldn't Play with Dead Things (2006) before it was diagnosed as being broken.
Jared Padalecki broke his wrist while filming a stunt during Season 2 of Supernatural. The writers ended up writing in that Sam had broken his wrist while fighting a demon in order to cover up Jared's cast.