The Boston Celtics will continue a feverish offseason roster overhaul by signing free-agent point guard Shane Larkin, according to a league source. Larkin, the No. 18 pick in the 2013 NBA draft, played 72 games with Saski Baskonia in Spain last season and averaged 13.8 points, 2.9 rebounds and 5.4 assists per contest. He elected to pass up a $6.3 million option to compete for a spot on a Boston roster that now features 16 guaranteed contracts. Larkin last played in the NBA with the Brooklyn Nets during the 2015-16 season. The Celtics, who have already formally signed nine players this summer, including All-Star Gordon Hayward and seven players on rookie deals, have revamped the roster of a 53-win team that advanced to the Eastern Conference finals last season. Boston made official Thursday the signings of 2016 first-round pick Guerschon Yabusele and German import Daniel Theis. Boston's other summer signings include veteran Aron...