Cumulative sum that resets based on the year

Question

I have a pandas df:

pd.DataFrame({\'team\': [\'ARI\',\'ARI\',\'ARI\',\'BAL\',\'BAL\',\'BAL\',\'BUF\',\'BUF\',\'BUF\'],
          \'year\': [2019, 2019, 2020, 2019