After his three goal debut, Grundy was used predominately in the forward line. Afer Grundy failed to convert his debut success on a consistent basis, Roos moved Grundy into defence where he has remained. It was only until 2009 that Grundy showed genuine promise as a defender. Grundy's ability to outmark his opponent (usually larger in weight and height) and find the ball more frequently, have been his most notable improvements.
In 2010, after Craig Bolton sustained a season-ending injury and then later on when Lewis Roberts-Thomson injured his hamstring, Grundy was called on by Roos to play on the competitions's best forwards. He marked players including Nick Riewoldt, Matthew Pavlich, Jonathan Brown, Barry Hall and Lance Franklin. He finished 5th in the Bob Skilton Medal.
2011 was another fairly consistent year for Grundy. He formed a stable partnership with Ted Richards as the Swans' key position defenders and held down the centre half-back position with aplomb. He was forced out of the Swans' run into and through the finals due to contracting glandular fever late in the year.