| ERA* Wins Losses Saves Games Games Started Complete Games Shutouts Innings Pitched Hits Allowed Homeruns Allowed Strikeouts Walks Allowed |
| Boston Losses - Single Season Leaders |
| Rank | Player | Year | Value |
| 1 | Earl Moore | 2016 | 12 |
| 2 | Dolf Luque | 2016 | 11 |
| 3 | Guy Hecker | 2017 | 10 |
| 4 | Earl Moore | 2017 | 9 |
| Orval Overall | 2016 | 9 | |
| 5 | Guy Hecker | 2016 | 8 |
| 6 | Pud Galvin | 2017 | 6 |
| 7 | Harry Byrd | 2017 | 5 |
| Jack Coombs | 2017 | 5 | |
| Herb Score | 2017 | 5 | |
| 8 | Spud Chandler | 2016 | 4 |
| 9 | Billy Pierce | 2017 | 3 |
| Pud Galvin | 2016 | 3 | |
| 10 | John Clarkson | 2016 | 2 |
| 11 | Dolf Luque | 2017 | 1 |
| Orval Overall | 2017 | 1 | |
| Reb Russell | 2016 | 1 | |
| Jack Coombs | 2016 | 1 |