Though the Diamondbacks felt it necessary to pull the plug on Cahill's season for now, there is some light at the end of the tunnel.
Cahill's first four starts this year were bad, even by 2014 Diamondback standards. He lost all four of his starts while Arizona was on their way to starting the season with a 5-18 win/loss record. He threw 17.2 innings with a 9.17 ERA and thirteen walks to go with seventeen strikeouts.
In light of his performance, Cahill was then relegated to the bullpen. Since then, he has appeared in fifteen games, thrown 23.2 innings, and kept his ERA at 3.04 with 10.27 K/9. The overall numbers still don't look good; 5.66 ERA, 5.44 BB/9, and just 0.1 fWAR on the year.
But there is reason to hope that this may have been simply a bad stretch for a pitcher on a team going through an even more miserable stretch.
For his career, Cahill has a K/9 rate of 6.09. In 2014, since he has been in the bullpen for most of his time, his rate has jumped to 9.58. His batting average on balls in play (BABIP) has generally hovered around the .280 to .290 mark. This season, it is .368, a number that is unsustainably high. By comparison, former starting pitcher and current Indians farmhand Kyle Davies, who holds the record for highest ERA for pitchers with at least 750 innings (5.56) had a career BABIP of .318.
The big issue has been the walks, as his career rate (3.53) is nearly two walks better than his rate this season (5.44), though he has certainly curtailed the issue slightly since being in the bullpen (4.56 as a reliever, 6.62 as a starter this year).
So this might be an issue of simply making a mechanical adjustment and trying to get him back on the road to being the consistent (if not necessarily exceptional) starter that he has been over the course of his big league career. That no team was willing to take a flyer on him speaks to the concern outside of the organization, along with the price tag associated with him.
If nothing else, Cahill has at least shown that he can be a good reliever, albeit an expensive one, at least for the next couple of seasons.