Baserunners' takeout slides at second base was a hot topic this offseason and Major League Baseball tweaked their rules just a bit as a result. It didn't take long for the Atlanta Braves to see the new rules in action.
Nick Markakis went in hard at second base in an attempt to break up a double play grounder off the bat of Hector Olivera in the seventh inning of Atlanta's opening day loss to the Nationals. Markakis was successful but was later ruled out because he was unable to stay on the base during the slide.
Harball Talk's Bill Baer goes into a little more detail:
Markakis slid past the second base bag. The new rules say "the runner is to slide so that he is able to or at least attempt to stay on the base". Seems like the ump got this one right.
So what looked like a bad call is probably the correct call. That still doesn't make it feel any better.