Pittsburgh Pirates : biggest year-to-year improvement/decline

Based on regular season win percentage:

                            Change in 
                              win %
Improvement: 1917 -> 1918      18.9   (33.1  ->  52.0)
Decline:     1909 -> 1910     -16.2   (72.4  ->  56.2)
Last Year:   2019 -> 2020     -10.9   (42.6  ->  31.7)