The 2015 Mets, featuring one young starting pitcher returning from Tommy John surgery and two starters in their first full MLB seasons, experimented with a six-man rotation in order to reduce pitchers' workloads. There's a good chance that the Mets could bring back the six-man rotation sometime in 2016, after Zack Wheeler returns.
The six-man rotation may be important this year, with several of the Mets' young pitchers coming off relatively heavy workloads. For Jacob deGrom, 2015 represented a jump of nearly 40 innings from his 2014 numbers (minors and majors combined). Entering last year, Harvey was penned for between 180 and 200 innings pitched—depending on whom you asked—and he threw 216. Noah Syndergaard fell just shy of 200 innings pitched. Steven Matz, who was injured for a good part of last year, threw 140 combined innings last year, the same as he did in 2014.
Taken together, it means that the Mets' front office—who will need good production from all four arms if they want to get to the postseason—may want to throttle their young starters a bit. Bartolo Colon, who signed a one-year deal in the offseason, may not be shuffled to the bullpen when Wheeler returns. Instead, he could be throwing every sixth day, especially if the Mets are in position to make a postseason run.
The six-man rotation wasn't popular among starters last year. Former starter Jonathon Niese, who was traded to the Pittsburgh Pirates for Neil Walker this offseason, told the Pittsburgh Post-Gazette that he's glad he won't be part of any future six-man rotation.
"You just never really got into a groove or a nice routine," he said. "They think the longer you go without throwing, the more rest you’ll get and the better you’ll feel. For me, that really wasn’t the case."