James Shields (C- with Padres, F with White Sox)
The Sox paid dearly when acquiring Shields, not in prospects but in performance from the number five spot in the rotation. With the Sox, Shields went 4-12, and had two months with an ERA over 11.00. His overall ERA with the Sox was 6.77, making him among the worst pitchers in the American League during that time.
For much of Shields career, he has had an average fastball/changeup difference of 8-10 MPH. Now, there is hardly a 6-7 MPH difference. On top of that, Shields fastball has decreased in velocity from 93-94 MPH in 2014 to 90-91 MPH this past season. The drop in velocity, plus a minor but large difference in his fastball and changeup will be key going forward for Shields.
Shields contract is very likely to become an albatross for the Sox, assuming he doesn’t develop elite fastball command. If Shields is unable to do that, expect another John Danks on the South Side. Something the Sox do not want to see for the next two seasons.