This season, the Oklahoma City Thunder are allowing eight points fewer per 100 possessions than the league average. That would be the most dominant defensive performance relative to the league in NBA history for a full season outside of Bill Russell’s Celtics (trailing 1963, 1962, 1965 and 1964)
The Thunder are genuinely one of the absolute most dominant defenses in history, and have taken a step forward after being seven points better than the average last year.
This season, the average is 115.3 points per 100 possessions, and they give up 107.3, boasting a number of elite defenders.
https://www.basketball-reference.com/teams/OKC/2026.html
https://www.basketball-reference.com/leagues/NBA_stats_per_game.html
Some other elite defenses that are close behind include the 04 Pistons and Spurs, the 25 Thunder, the 08 Celtics and the mid 90s Knicks (as well as a bunch of 60s Celtics teams).
The most dominant regular season team ever by this metric is the 64 Celtics, who gave up an estimated 10.8 fewer points per 100 possessions than the league average.
The Celtics’ defensive rating ranks in the league from getting Cousy in 1950 through Russell through the career of another great defensive center in Dave Cowens who helped win two championships was as follows:
Cousy, before Russell: 10th, 4th, 8th, 8th, 8th, 6th,
Russell: 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 1st, 2nd, 1st,
Post-Russell: 8th, 3rd, 5th, 1st, 6th, 3rd, 3rd, 7th, 12th, 19th, 4th