I have this pandas data frame named df

Code:
data = {'Team':['ATL', 'BOS', 'CHI', 'ATL', 'CHI','CHI'],
        'PTS':[95,90,92,91,88,99,],
        'Game':['x','x','x','x','x','x']}

df = DataFrame(data)
I would like to keep a running count for each Team in the Game column.

So that the output is like this
Team PTS Game
ATL 95 1
BOS 90 1
CHI 92 1
ATL 91 2
CHI 88 2
CHI 99 3

I can't get the pandas rolling_count function to work right so I need make a loop. There a numerous examples on how to make a for loop in python but not many at all about looping through dataframes.