From 2005 through 2011, Dan Haren was a very good pitcher. Over those seven seasons, he compiled 34.6 fWAR, the third-best mark in baseball among starting pitchers, thanks to a good strikeout rate and a superb walk rate. He gave up home runs at a less-than-ideal clip, but he wasn't getting shelled on a regular basis.
As a result, he posted a 3.50 ERA and 3.52 FIP. His 82 FIP-, a stat that's adjusted for league and ballpark, suggests he was 18 percent better than the league-average pitcher over that span. That's not quite as elite as his wins above replacement, but it's still impressive.
The last two years—his age-31 and age-32 seasons—have been rough for Haren, though. Among 72 qualified starting pitchers, his 4.51 ERA was the seventh-worst mark in the game. His strikeout and walk numbers were still close to his career norms, but he's been giving up home runs at a rate of 1.46 per nine innings, an alarming clip. It's no surprise that his average fastball over the last two years has traveled at roughly 88.7 miles per hour. That's a significant drop-off from the roughly 90.3 miles per hour he threw in 2010 and 2011.
Originally drafted by the Cardinals, Haren's been all over the place in his career. St. Louis traded him to the Oakland Athletics in 2004 as part of a package for Mark Mulder. The A's flipped him to the Diamondbacks in a deal that netted Oakland Carlos Gonzalez—yes, the Carlos Gonzalez currently of the Rockies—in 2007. And Arizona traded Haren to the Angels in 2010 for Patrick Corbin, Rafael Rodriguez, Joe Saunders, and Tyler Skaggs.
With all that mileage, Haren finally hit free agency after last season, which was at that time the worst year of his career. He signed a one-year, $13 million with the Nationals before the 2013 season and is now a free agent.
Haren just hasn't been the pitcher he used to be over the past two years. It wouldn't be a shock to see him get more than one year in his next contract, but his average annual salary could drop a bit after a second straight down year. His 4.67 ERA this year might not sound terrible, but in a season that saw very few runs scored overall, it was pretty bad. Washington did not offer Haren a qualifying offer, which means he won't cost a new team a draft pick.
Citi Field has a bit of a reputation as a pitcher's park, even though it's not an extreme one, which could appeal to Haren. The Mets have a couple of spots open in their rotation, and Haren at least looks capable of filling one. It's hard to imagine he'll ever regain the ability he had when he threw harder, though. The Mets can likely find similar production for less money than Haren will receive this winter, but if he can be had at a relative bargain, he might make sense for Sandy Alderson.