This was expected. The Mariners sent Corey Hart to the disabled list with a hamstring injury, and did a straight one for one swap with Nick Franklin. I wrote about this extensively yesterday as if it had already happened, so check that out if you haven't read it already.
Franklin is likely to see playing time nearly every day now, moving all over the field or simply taking Hart's place at DH. Logan Morrison should return in the next week or two, and along with James Paxton, that might start another domino effect of players moving down, including Brad Miller. Miller has survived this round of transactions (at least for now), but it would hardly be a surprise to see Franklin spell Miller at shortstop here and there over the next few weeks. If not, Miller will be given another stretch to pop out of his slump. I don't see the point anymore, but ad nauseam - he's here, he's broken, and that's that.
There's no excuses for Nick Franklin this time, as it's once again time to prove whether he can make the jump or not. His destruction of AAA was impressive, but contact has always been an issue for him at the big league level. If he makes the leap to the bigs like he did when he was first recalled in 2013, this could easily be an upgrade for the Mariners offense, along with additional flexibility around the diamond. Translation: less Willie Bloomquist. Maybe. Probably not.
Hart's injury has officially been classified as a grade 2 hamstring strain, which means he's probably going to be out longer than the minimum 15 days. The usual diagnosis for an injury like this is anywhere from three to four weeks, but given Hart's age and recent injury history, it would hardly be a surprise if this kept him out until the All-Star break. It's the same injury that kept a young, relatively healthy Giancarlo Stanton out for 37 games last year. Hamstring injuries are always a bit different for everyone, and it's all about the setbacks -- sometimes you end up like Matt Kemp and are plagued for months, and other times there's no setbacks and you come back right at the projected timetable. Even though Hart is old and slightly brittle now, it would be unfair to conclude the worst. But it's hardly unfair to expect it.