Well, if we're being pedantic. Wouldn't it be a field promotion since Riker is already a commissioned officer? A field commission refers to enlisted personnel being temporarily promoted to an officers rank. Riker might have been made a Brevet Captain. Brevet being a term for a temporary promotion. For example, George Custer was made a Brevet Maj. General in the Civil War, but reverted to being a Captain after the war and died Lt Colonel at Little Bighorn.