KC was a great PG. RIP. He was about assists and defense. That was his role. He shared the backcourt in the 60s with Sam Jones, one of the greatest scorers in Celtics history. The great golden era of the Russell Celtics. The "Jones boys" (from the hit song in the 60s), as Johnny Most affectionately called them, were the successors of Cousy-Sharman, another great Celtics backcourt of the 50s. The Celtics in those days were a complete team, led by Bill Russell. Nobody could beat them.
KC later coached the Bird Celtics--another great era, though shorter because of McHale and Bird's curtailed careers. He won a couple of championships with them, but should have won more. Red's successor as GM never heeded Bird's advice of adding a couple of good bench players, and they lacked the depth. The result was Larry and Kevin were overplayed, and ultimately broke down.