John Maine has been quite the enigma the past couple seasons. After having a bone spur removed from his throwing shoulder in 2008, the Mets believed that Maine would be a contributing member to the 2009 pitching rotation. This was not meant to be, as Maine would miss the majority of the 2009 season with arm fatigue and an assortment of unrelated injuries and setbacks. A career 4.59 xFIP and at his best a 2.7 WAR pitcher, Maine has been suffering from fatigue almost his entire career. He missed time or had decreased production every season since his 191 inning season in 2007.
There is obviously some sort of conditioning or arm issue with Maine. If you look at his splits over the course of his career it appears to be a very large gap between his first half and second half performance. Using very simple metrics, it's pretty obvious that there is some sort of severe split. In the first half, over a sample of 295 innings, Maine has a 3.68 ERA. In the second half, it inflates all the way up to 4.85. This definitely shows that his arm fatigue issues have a pretty sizable effect on the quality of his pitching.
His worst months are August and September/October, usually once Maine hits higher than 100 innings. In August, his ERA is 4.87 and September/October 5.66. This is compared to earlier in the season when his ERAs are 3.16, 3.75, 4.00, and 3.68. ERA doesn't tell the full story about a pitcher and can be influenced by outside sources (like poor defense or an extreme bout with bad luck) but these numbers make it obvious that once Maine hits a certain number of innings he cannot continue the same production.
His velocity also jumps around a lot over the course of the season. Looking at graphs of his average velocity over the course of a season on fangraphs, you can see a drop half way through his seasons. Using 2008, his pitches earlier in the season average from 93-91, while toward the end of the season it dips to around 91 consistently, which fits into his full season average (92.3 in 2008, which dipped to 91.2 in 2009). He is obviously losing velocity on his fastball due to fatigue, especially proven when the graphs show a dip toward the end of his graph.
As I said in my previous article, Jon Garland is the kind of pitcher that John Maine should be this point in his career. They both put up similar production numbers (Maine: 4.59 career xFIP, Garland: 4.61 xFIP) but Maine cannot stay healthy. Garland's value is in his durability. Maine may be slightly a better pitcher but his inability to stay in a rotation throughout an entire season hurts his value immensely. When you consider how desperate the Mets are for solid pitching you can see why losing out on Garland is a little bit of an issue. It's not the end of the world but that depends on who else the Mets sign and if Maine can stay healthy.
It's not obvious how the Mets' rotation is going to shake out right now but I honestly don't believe that Maine should be starting at this point. He should be put into a position where his innings can be controlled and his value the highest and position is in the bullpen. His stuff is good enough when he's healthy to make a very effective arm out of the bullpen and could even spot start when necessary. This would make him the best pitcher possible.
Considering the importance of relief pitching which would you rather have: 100 IP of 3.80-4.3 xFIP pitching out of the pen or 150 innings of 4.59 xFIP starting when you run the risk of injury and further fatigue? If he's so good at the beginning of the season and so awful at the conclusion it makes much more sense to use him as a reliever. It will spread him out over a season and preserve him. He's not being used properly if he continues to suffer from dead arm and fatigue. It just doesn't help Maine or the Mets at all.
Maine is a good pitcher and shouldn't be given up on. He's a positive WAR pitcher when healthy and able to throw more than 150 innings. However, since in recent years he's shown that he's unable to do this, he should be slotted into the pen. Then the fatigue issues won't creep up on him and cost the team games late in the season. Instead, he'll be healthy and able to contribute to a team in desperate need of pitching help.