Span, 28 (is he really only twenty-eight? seems like he's been around much longer than that, but maybe that's just me), has spent five seasons in the Majors with the Twins, which drafted him in the 1st round of the 2002 MLB Amateur draft.
Blocked by then-Twin CF Torii Hunter, Span spent considerable time in the Twins' farm system, spending 6 years toiling throughout Elizabethon, Quad Cities, Fort Myers, New Britain, and Rochester. He was brought up in 2008 and has since been a reliable but frustratingly average force in the outfield, hitting .284/.357/.389. Span has just 23 home runs in 5 professional seasons.
Meyer, 22, was drafted by the Boston Red Sox in 2008 and again by the Nationals in 2011, 23rd overall. In one minor season and 129 innings pitched, Meyer posted a 2.86 ERA while striking out 9.7 (that's NINE POINT SEVEN) per nine innings.
The Nationals get Span for the last two seasons of his 5-year, $16.5M contract that includes a $9M club option for 2015.