Late last month, the Boston Celtics were struggling along in the middle of the NBA standings. They weren’t great and they weren’t awful, but they were predictable—predictably middle of the pack. But star point guard Rajon Rondo was having another terrific year, racking up triple-doubles (achieving double digits in scoring, rebounds and assists) at twice the rate of his closest rivals. He was the Celtics top performer and the key to what limited success they were having....