With the default league totals and with the option checked for having it change every here, here's my top 5 Season .AVG's:
1. Luis Polonia .4443 - 1989
2. Hugh Duffy .4397 - 1894
3. Rick Miller .4350 - 1975
4. Dave Cash .4347 - 1973
5. Dave Cash .4293 - 1970
Dave Cash hit .400 8 Times!
Most of the players over .400 have been since 1960.