Best starting pitching depth

Rick Porcello would be a No. 3 starter on many teams, but he's insurance for Detroit. Rick Osentoski/US Presswire

When Opening Day rolls around in a few months, teams will have to declare an active 25-man roster. That roster will, in most cases, be divided into 13 position players and 12 pitchers, with five pitchers designated as starters and the rest serving as relievers out of the bullpen.

However, while teams will begin the season with five starters, any team with a strong hope of contending in 2013 should have a good sixth starter waiting in the wings.

Because of the frequency of pitcher injuries, it is exceedingly rare for a team to make it through the whole season without leaning on a starter who didn't begin the year in their rotation. Last year, 186 pitchers threw at least 50 innings as a starter, which works out to an average of just over six per team. While the sixth starter often begins the season in Triple-A or in long relief, he will usually end up throwing nearly half a season's worth of innings, and his performance can make a significant difference on a team's final record.

For instance, A.J. Griffin didn't join the Oakland Athletics until June 24, when he was called up from Triple-A Sacramento to replace the injured Brandon McCarthy. He proceeded to post a 3.06 ERA in 15 starts over the remainder of the season, and the A's went 12-3 when he took the hill. The A's beat out the Rangers for the AL West title by one game. While no single player can be responsible for a division title, it is pretty clear that the A's wouldn't have finished ahead of the Texas Rangers had Griffin not put together a remarkable second half of the season. Kris Medlen, Michael Fiers, Alex Cobb and Hisashi Iwakuma also made significant contributions to their teams after joining the rotation in midseason.

So which teams are prepared for the inevitable need for a sixth starter heading into 2013? Here are three pitchers who give their teams necessary depth and could end up being big parts of a winning club even if they don't have a job coming out of spring training: