WALTHAM, Mass. — Boston Celtics general manager Danny Ainge thought Doc Rivers was going to be the next Gregg Popovich, Jerry Sloan or even Red Auerbach — coaches who stayed with one team for decades.

Rivers got the nine-year itch.

“He felt like it was time for a change. He felt like we all needed a change,” Ainge said on Tuesday night after the deal to allow Rivers out of his contract to coach the Los Angeles Clippers was final. “That was his rationalization, or justification, for going to the Clippers: that this was better for everybody.”