Bregman on 2nd, McCann on 1st. Marwin singles on a ground ball to RF, throw goes toward the plate but is awful and gets cut. McCann had rounded 2nd far enough to convince Marwin that he was going to 3rd, but he stopped and went back to 2nd, leaving Marwin in no man's land between 1st and 2nd, where he eventually got tagged out.
The ball wasn't deep enough or slow enough for McCann to drag his ass to 3rd. Neither he nor Marwin should have ever been more than 10 ft off their bag. It was bad baserunning.