I'm not the type to admonish either action, though I guess if I had to weigh the two offenses, I'd put the not hustling on a grounder as more of a no-no if only because of intent. It's not like if someone told Rosario the second the ball left his bat that it was going to hit the wall he wouldn't have sprinted out of the box, I'm sure he would have been all smiles had he gotten a triple. On the other hand, conceding a grounder is willfully choosing not to take the chance that the fielder may bungle the play, which isn't out of the realm of possibilities. But again, I'm not a hardliner on this stuff, I've come to accept both as atypical but still common elements of the game and I'd do little more than roll my eyes.