I will never understand why Chris Sale was signed after the 2018 season when he had another year left on his contract. Sale was already showing some signs of losing effectiveness later in seasons when the Red Sox acquired him in 2017, as the following chart showing his monthly ERA's with the White Sox shows:
With the Red Sox, Sale's late season struggles were exacerbated. Sale was an exceptional pitcher in his first year with the Boston (2017) through the end of July,
with a 13-4 record, 2.37 ERA and 1.92 FIP. But he struggled in August, September, and the postseason of that season, going a combined 4-6 with a 4.70 ERA. The cracks were showing, with even more evidence he no longer could be relied on to pitch effectively for a full season. Then in 2018 Sale again started strong, going 11-4 with a 2.04 ERA (2.02 FIP) through the end of July, followed by him being effectively shut down, with only 17 IP in August and September. He was a non factor that year in the postseason, as well, with just 3 starts, only 15 1/3 innings, and 7 earned runs allowed (4.11 ERA). Overall with the Red Sox in the postseason, Sale is 1-3 with a 6.35 ERA.
Why anyone would even consider signing Sale after the 2018 season a year before his contract was up, when he was clearly struggling to finish the prior 2 seasons and showed a tendency his entire career to wear down, is a mystery. I think it's the worst signing in team history.
An aside, but we saw something similar with Tuukka when I first joined the Bruins (declining play after x games played), and made a conscious effort to limit his regular season starts, going as far as to go through the schedule well before the season started to look for games when the back-up goalie made the most sense statistically. It's a different sport, and I'm not sure that would work in baseball, but the Red Sox certainly should have been aware that Sale's effectiveness diminished later in seasons and taken whatever necessary precautions. Signing him to a 5 year contract was not one of them.