Wednesday was one of those nights when we’re reminded Avery Bradley is 22 years old and in his third year in the NBA. As one of the best on-ball defenders in the NBA, his importance to the Celtics is unquestioned, and Doc Rivers was banking that he would provide resistance to Brooklyn guard Deron Williams, who when healthy is one of the league’s best because he can shoot from the perimeter and bounce off defenders without a dent. When Bradley attempted to defend Williams, the blame for whatever contact ensued was assigned to Bradley, who picked up two fouls in the first 3:44, and then his third with four minutes left in the half. Thirty-nine seconds into the second half, Bradley, eager for another opportunity against Williams, was whistled for his fourth foul when the two collided and their feet tangled, causing Williams to tumble. That call infuriated Bradley. He stood there, arms raised, looking at official Sean Corbin with an expression of helplessness. It was a rare occasion when Bradley was taken out of his game defensively, losing his edge because his aggressive defense was hindered by tight officiating. After his fourth foul, Bradley sat near the end of the bench to cool off, putting his warm-up back on, a sign that his respite would be extended. He was confused and irritated. Veteran teammate Jason Terry attempted to calm him down by offering pointers on how to defend Williams. It was the first time this season Bradley and Williams faced off because Bradley missed all three previous meetings recovering from surgery on both shoulders. The Celtics lost, 101-93, and the game was not that close. Williams finished with 29 points and 12 assists, setting the tone for the Nets’ offense. His dribble penetration freed up teammates for open shots, and the Celtics’ defense crumbled. Bradley’s defensive prowess is no longer a secret. Opposing teams have figured out two ways to unnerve him: pressure him as much as he pressures them or use his aggression to get him into foul trouble. The Nets went with the latter as Williams knew the key to breaking down the Celtics was to eliminate Bradley.