Rivals is an insert set in 2004 Leather and Lumber. Each card has two players who were considered rivals during their careers. The card backs describe how the two are connected in baseball history in a short paragraph. The base set was serial numbered to 2499 copies each and paralleled with a silver set serial numbered to 100. The set was also partially paralleled with a dual game used set (only cards 6 and 37 were not paralleled). The Materials set were serial numbered as well with print runs ranging from 250 to 20. All the cards were randomly inserted into packs.