[NBC Sports Boston] - Five biggest X-factors for Celtics who could spark another title run

Every NBA champion has one or two superstars who play a significant role in their team lifting the Larry O’Brien Trophy, but winning 16 games over four playoff rounds doesn’t happen without supporting players stepping up along the way. There are a couple games every playoff run that require someone to come off the bench and provide a spark offensively. The Celtics know this fact better than most franchises. Don Nelson hit a clutch shot toward the end of Game 7 in the 1969 NBA Finals.