1In [41]:
2df.loc[df['First Season'] > 1990, 'First Season'] = 1
3df
4
5Out[41]:
6 Team First Season Total Games
70 Dallas Cowboys 1960 894
81 Chicago Bears 1920 1357
92 Green Bay Packers 1921 1339
103 Miami Dolphins 1966 792
114 Baltimore Ravens 1 326
125 San Franciso 49ers 1950 1003