Notre Dame is a great defensive team not because they are physically imposing or lightning quick, but rather because their communication is such that their opponents wind up being a step behind them. That forces quick shots, tough shots and reduces connecting plays.
The Irish also work the ball to the high post in order to relocate out to open shooters or cutters and thus defeat a zone defense. ND also has its defenders remain stationary near the basket in order to draw fouls.
The keys for UConn are to defend without fouling, to be quick on switches in screens, good ball movement and reversal to find open players, and to hit three point shots.