In a surprising move, Nationals manager Jim Riggleman has resigned, according to MLB.com's Bill Ladson (Twitter link). Riggleman stepped down after his club beat the Mariners this afternoon and improved to 38-37 thanks to an impressive stretch over the course of which they've won 11 of 12 games.
The manager, who was in the final year of his contract, told GM Mike Rizzo that he would resign if his contract situation wasn't resolved, according to Adam Kilgore of the Washington Post (Twitter link). Riggleman's agent, Burton Rocks, told Jon Heyman of SI.com that "they should have picked up the option" and that "it wore on Jim." Riggleman will manage again, according to his agent (Twitter link).
Rizzo had discussed picking up Riggleman's 2012 option, but felt the time wasn't right, according to Ben Goessling of MASNsports.com (Twitter links). The GM called Riggleman's decision "very disappointing to the players, fanbase, city and [himself]."
It's the second time this week that an NL East manager has resigned; Edwin Rodriguez of the Marlins stepped down over the weekend.