Typically, Manager of the Year laurels go to the skipper whose team did the best job of defying expectations for the better or overcoming unanticipated obstacles. That, then, will inform our choices in most cases.
As a reminder, these are predictions of who will win based on the season to date and not statements of who deserves to win ...
Clint Hurdle, Pirates: With their next win, the Pirates will clinch their first winning season since 1992. As for the greater goals, they presently have, per CoolStandings.com, a 99.4-percent chance of making the postseason. Should that come to pass -- the Pirates' making the playoffs, that is -- then Hurdle gets the hardware without argument. So give him a 99.4-percent chance of winning.
Freddie Gonzalez, Braves: Gonzalez's team has the best record in all of baseball despite injury upon injury to core contributors (Tim Hudson, Jason Heyward and two key lefty relievers among them). Sure, a relatively breezy schedule has helped, but Gonzalez and the Braves have vanquished the Nats and overcome the unforeseen in a big way.
Don Mattingly, Dodgers: The Dodgers had high expectations coming into the 2013 season, and Mattingly's club has lived up to them (and then some). However, it's the way in which they've lived up to them -- 9 1/2 games out on June 22 to 12 1/2 games up at this writing -- that makes Mattingly a contender. He went from being fired at any moment to helming a World Series contender. Funny things happen over the course of 162 games.