All of the Medals that you earn in Franchise mode are based on team stats, and where you finished in these categories in the league.

Gold = 1st
Silver = 2nd
Bronze = 3rd

Great Glove - best fielding %
Pitching Ace - best ERA
Strikeout King - most Ks
Speed Demon - most SBs
Golden Slugger - most HRs
Batting Champ - best batting avg.
Dominant Team - Most wins in regular season
Cellar Dweller - Most Losses in regular season
Tightwad - least BP spent
Big Spender - most BP spent

To dress your team in classic uniforms, go to the Setup screen and change the Uniform selection from Standard to Classic.