Matt Cain was once considered the horse of the Giants rotation. From 2007 through 2012, he pitched at least 200 innings, and only missed that mark by 15.2 innings in 2013. The following season ended early for Cain, as he had to undergo surgery to remove bone chips in his elbow.
Fortunately nothing was structurally wrong with his UCL or anything else that could cause lasting damage, but since his return in early July, Cain simply hasn't been an effective major league starter. He's given up home runs at a startlingly high rate, and today, he was placed on the 15-day DL due to what the Giants are calling "elbow nerve irritation".
In 52.2 innings this season, Cain has a 6.15 ERA, a 5.59 FIP, and a SIERA of 4.56. While at first, it seemed that he simply needed a few starts to iron out his mechanics, that hasn't proven to be the case at all. In fact, he's gotten worse in his recent outings, as his 8.03 ERA, and 7.30 FIP in the month of August indicate. Fortunately for Cain, there doesn't appear to be anything seriously wrong with his elbow, and assuming he's healthy, he could return before the season is over.
Cain had a cortisone shot, said arm was a little "achy" after last start. Hopes to be back next month. Good news was MRI came back clean.— Alex Pavlovic (@AlexPavlovic) August 28, 2015
However with a full rotation, and Tim Hudson and Tim Lincecum waiting to come off the DL (which will likely happen on September first), Cain might not be able to work his way back in. Ryan Vogelsong has pitched well in the month of August, and Chris Heston, the author of 2015's first no-hitter, has been recalled to take Cain's spot. Heston's demotion was the result of needing to work on his mechanics, and giving the right-hander some rest for the stretch run, as he was well on his way to passing his career high in innings pitched.
With a crowded staff, and Cain severely underperforming, he might have already thrown his last pitch of 2015. He's signed through the 2017 season, which likely means that the Giants will be incredibly careful as to how they approach the handling of his elbow. Cain is owed at least $49.5 million (he has a buyout worth $7.5 million for 2018) through the 2017 season, and the Giants won't push him harder than they need to as the season comes to an end.