The Boston Celtics have started this season with a lot more depth than most were expecting. The second unit is filled with rookies and inexperienced players, with Marcus Smart and Terry Rozier being the only ones who had ever played together before. There were good reasons to question whether or not that unit could hold up, and they certainly have so far.
The second unit has been a big part of the great start to the season, but it is not all positive. One of the biggest reasons the Celtics are the best defense in the league is that second unit.