The Cleveland Cavaliers did not have a good year on the defensive end in 2016-17. They were 22nd overall in defensive rating, compared to being 10th the year before (per nba.com). There were a multitude of factors that went into that drop-off, and one of those was the lack of rim protection. The Cavs were just 23rd in blocks per game last season, according to teamrankings.com.
In addition, they gave up over four more paint points per game to opponents compared to the year before, and that really hurt their defensive efficiency, which dipped to 22nd in the league.