The news, as broken by John Gambodoro on Twitter and confirmed by Jon Heyman, Steve Gilbert, and Ken Rosenthal, is that the D-backs have traded second baseman Kelly Johnson to Toronto for second baseman Aaron Hill and shortstop John McDonald. Johnson, mired in a slump that saw him benched for four of five games recently, had apparently fallen out of favor the D-backs, who had clearly become disinterested in trying to retain Kelly. Since August 8, Kelly had hit .154/.195/.256, going 6-39 with two doubles, a triple, two walks, and 11 strikeouts, seeing his season OPS drop below .700 in the process. Kelly's .214 BABIP in that span is low - as is his .254 figure on the year - but the team decided it couldn't wait for Johnson to break out of his slump while in the midst of a playoff chase.
In Hill, the D-backs get a replacement second baseman for the rest of the season who has struggled immensely since his breakout .286/.330/.499, 115 wRC+ 2009 season in which he clobbered 36 home runs in 734 plate appearances. Hill slumped to a .205/.271/.394 line in 2010 (.196 BABIP), seeing his wRC+ drop all the way down to 77, but still managed to knock 26 long-balls to keep his value relatively afloat. In 2011, though, Hill's power has largely collapsed, hitting .225/.270/.313 with just six home runs through 429 plate appearances. According to FanGraphs, Hill has been half a win below replacement level thus far in 2011.
According to Cot's Baseball Contracts, Hill has a pricey $8MM club option for 2012 that is the first of two such options (there were initially three options, but in order for the third option be in place, all three needed to be simultaneously exercised prior to the 2011 season). If his 2012 option is exercised, his 2013 option will be for another $8MM. No word as to whether the club has any intention of exercising these options, or if they're entertaining the (scary) idea of offering arbitration after this year in order to try to get a compensatory draft pick.
McDonald gives the D-backs another shortstop to replace the long-injured Stephen Drew, particularly with Willie Bloomquist (for the sake of news, I'll refrain from using
awesome nicknames) struggling mightily as of late. McDonald has been a useful reserve the last couple of seasons, posting a 66 wRC+ in 182 plate appearances (65 games) so far in 2011. On the plus side, McDonald is a very good shortstop, with a career 5.9 UZR/150 in over 3,000 innings at the position in his career. McDonald will be a free agent at the end of the season.
Kelly is also on the fringes of being a Type A free agent, and Toronto GM Alex Anthopoulos seems more content offering him arbitration to try to get a pick than declining Hill's option and offering him arbitration. Kelly's salary in 2011 is $5.85MM, compared to the $5MM owed to Hill this year. All three players either had cleared trade waivers or were claimed by the other team involved in the deal in order for the trade to go through.