The Washington Bullets have the best defensive rating by a team in a season, with a 91.3 rating in 1974-75.

best defensive rating by a team in nba history in a single season

TEAM	DRTG	SEASON	GP	MPG	PPG	RPG	APG	SPG	BPG	TPG	FGM	FGA	FG%	3PM	3PA	3P%	FTM	FTA	FT%	MIN	PTS	REB	AST	STL	BLK	TOV	PF
Washington Bullets	91.3	1974-75	82	241.5	104.7	47.5	24.5	11.3	5.0	19.4	43.4	93.9	46.2				18.0	23.9	75.2	19,805	8,585	3,897	2,005	929	409	1,594	1,961
Chicago Bulls	93.6	1973-74	82	241.2	102.0	45.8	22.8	9.3	3.9	20.6	40.1	90.0	44.6				21.8	28.2	77.1	19,780	8,368	3,759	1,868	764	316	1,690	1,874
Milwaukee Bucks	93.6	1973-74	82	240.9	107.1	49.0	27.1	8.9	6.3	20.7	45.4	92.3	49.2				16.2	21.2	76.3	19,755	8,780	4,014	2,225	726	519	1,694	1,864
Detroit Pistons	93.8	1973-74	82	240.9	104.4	47.3	23.9	9.7	5.1	21.5	42.1	91.6	45.9				20.2	26.4	76.4	19,755	8,560	3,881	1,956	793	419	1,763	1,930
San Antonio Spurs	94.1	2003-04	82	240.9	91.5	45.1	20.4	8.1	6.5	14.7	34.7	78.5	44.2	5.0	13.9	35.8	17.2	25.2	68.1	19,755	7,501	3,698	1,676	661	537	1,203	1,667
Capital Bullets	94.2	1973-74	82	240.6	101.9	50.9	21.6	8.6	5.4	19.1	42.4	96.2	44.1				17.0	22.8	74.5	19,730	8,353	4,173	1,770	703	441	1,568	1,746
Chicago Bulls	94.4	1974-75	82	242.4	98.1	47.5	22.4	8.1	4.6	18.1	38.6	86.4	44.7				20.9	26.9	77.7	19,880	8,045	3,893	1,840	668	379	1,482	1,952
Golden State Warriors	94.5	1975-76	82	241.8	109.8	52.0	24.9	11.3	5.1	19.7	45.0	97.3	46.2				19.8	26.3	75.1	19,830	9,002	4,261	2,041	928	416	1,613	2,022
Boston Celtics	94.7	1974-75	82	240.9	106.5	52.0	26.3	8.1	3.5	19.8	43.7	95.4	45.8				19.0	24.0	79.1	19,755	8,734	4,264	2,159	662	288	1,625	1,913
New York Knicks	94.7	1973-74	82	241.2	101.3	44.9	23.6	6.8	3.4	17.8	42.4	91.3	46.5				16.5	21.2	77.7	19,780	8,306	3,684	1,937	554	277	1,463	1,884
San Antonio Spurs	95.0	1998-99	50	241.5	92.8	44.0	22.0	8.4	7.0	15.2	34.8	76.2	45.6	3.4	10.4	33.0	19.8	28.3	69.8	12,075	4,640	2,198	1,101	421	351	759	1,010
Boston Celtics	95.1	1973-74	82	241.2	109.0	54.3	26.7	6.8	3.7	21.9	44.3	97.2	45.6				20.5	25.6	80.0	19,780	8,937	4,452	2,187	561	305	1,796	1,868
Washington Bullets	95.3	1975-76	82	242.7	102.8	46.7	22.2	8.5	5.9	20.4	41.7	88.2	47.2				19.5	27.0	72.0	19,905	8,427	3,831	1,823	696	485	1,672	1,921
Detroit Pistons	95.4	2003-04	82	241.2	90.1	42.8	20.8	8.0	7.0	15.1	33.5	77.0	43.5	4.1	11.8	34.4	19.0	25.3	75.3	19,780	7,388	3,506	1,702	659	570	1,241	1,664
Denver Nuggets	96.1	1976-77	82	241.2	112.6	48.6	27.6	11.6	5.7	24.5	43.8	91.1	48.1				25.0	33.9	73.8	19,780	9,233	3,988	2,262	953	471	2,011	2,142
Los Angeles Lakers	96.6	1973-74	82	240.9	109.2	52.9	26.6	9.7	8.0	23.3	43.1	95.2	45.3				22.9	29.8	76.9	19,755	8,951	4,335	2,179	794	653	1,913	2,032
Boston Celtics	96.7	1975-76	82	240.9	106.2	52.9	24.1	6.8	3.2	19.6	43.0	96.4	44.6				20.2	25.9	78.0	19,755	8,708	4,341	1,980	561	260	1,609	2,002
Phoenix Suns	97.0	1977-78	82	241.2	112.3	45.7	28.5	12.9	4.5	21.5	45.5	95.6	47.6				21.3	28.4	75.1	19,780	9,211	3,745	2,338	1,059	372	1,766	1,956
Cleveland Cavaliers	97.0	1975-76	82	241.5	101.7	46.1	22.5	7.8	4.8	16.2	42.6	94.0	45.4				16.4	22.3	73.7	19,805	8,340	3,780	1,844	638	397	1,330	1,871
Kansas City-Omaha Kings	97.1	1974-75	82	240.6	101.4	45.6	22.6	8.8	4.2	18.8	39.7	88.5	44.9				21.9	26.7	82.1	19,730	8,311	3,736	1,853	724	347	1,542	1,968
Atlanta Hawks	97.1	1998-99	50	241.5	86.3	43.5	15.6	6.9	5.2	14.9	30.8	75.2	40.9	3.9	12.9	30.6	20.8	28.4	73.1	12,075	4,315	2,175	782	346	260	745	987
Portland Trail Blazers	97.2	1977-78	82	240.6	107.7	47.2	25.2	9.7	4.8	19.8	43.4	89.8	48.3				20.9	27.5	76.0	19,730	8,829	3,873	2,067	798	390	1,625	2,068
Indiana Pacers	97.2	2003-04	82	241.5	91.4	41.7	21.6	8.9	5.0	14.4	33.6	77.1	43.5	5.5	15.6	35.1	18.8	24.6	76.4	19,805	7,493	3,417	1,774	726	411	1,182	1,709
Golden State Warriors	97.3	1974-75	82	241.2	108.5	52.1	25.3	11.9	4.5	20.9	45.3	97.3	46.5				17.9	23.4	76.8	19,780	8,898	4,270	2,076	972	365	1,716	2,109
Chicago Bulls	97.4	1976-77	82	241.5	98.9	48.7	24.3	8.5	4.4	18.9	39.6	87.6	45.2				19.7	26.3	74.7	19,805	8,111	3,997	1,989	699	364	1,552	1,871