If you want an Galaxy S5 Active, your only choice is AT&T. Meanwhile, the newly announced Galaxy S5 Sport is a Sprint exclusive. Of course, these are pretty much the same phone with tiny aesthetic differences. Sprint is really pushing the fitness angle, though.
The GS5 Sport has the same trio of physical buttons on the front as the Active, and the specs are the same. You can get the gist simply by reading up on the Active, and pretending it says "Sport." It's IP67 rated for water and dust resistance, and it's got a beefier, more textured casing than the regular GS5.