Ben Wallace has the lowest defensive rating in a season, with an 87.5 rating in 2003-04.

lowest drtg in a single season
Interpreted as:
lowest drtg with a minimum of 2000 minutes played per 82 team games by a player in a single season
2003-04Wallace1974-75Hayes1998-99Robinson1973-74Lanier1974-75Unseld2003-04Duncan1973-74Hayes1973-74Abdul-Jabbar1973-74Ray1976-77Jones1975-76Abdul-Jabbar2002-03Wallace1973-74Cowens1974-75Thurmond2000-01Camby1974-75Cowens1973-74Perry1975-76Hayes1998-99Ewing1976-77Walton1974-75Lacey2003-04Garnett1998-99Duncan1973-74Smith1974-75Sloan87.587.788.088.088.488.588.788.889.389.990.090.090.490.590.590.791.091.191.291.391.591.591.591.691.6
NAMESEASONTMGPDRTGMPGPPGRPGAPGSPGBPGTPGFGMFGAFG%3PM3PA3P%FTMFTAFT%MINPTSREBASTSTLBLKTOVPF+/-
Ben WallaceBen Wallace2003-04DETDET8187.537.79.512.41.71.83.01.53.99.242.10.00.112.51.83.649.03,0507731,006138143246123162+437
Elvin HayesElvin Hayes1974-75WASWAS8287.742.323.012.22.51.92.39.020.344.35.06.576.63,4651,8871,004206158187238
David RobinsonDavid Robinson1998-99SASSAS4988.031.715.810.02.11.42.42.25.510.850.90.00.00.04.97.465.81,55477549210369119108143+331
Bob LanierBob Lanier1973-74DETDET8188.037.622.513.34.21.43.09.218.350.44.05.079.73,0471,8221,074343110247273
Wes UnseldWes Unseld1974-75WASWAS7388.439.89.214.84.11.60.93.77.550.21.72.568.52,9046721,07729711568180
Tim DuncanTim Duncan2003-04SASSAS6988.536.622.312.43.10.92.72.78.617.150.10.00.216.75.18.559.92,5271,53885921362185183164+543
Elvin HayesElvin Hayes1973-74CAPCAP8188.744.521.418.12.01.13.08.520.142.34.46.172.13,6021,7351,46316386240252
Kareem Abdul-JabbarKareem Abdul-Jabbar1973-74MILMIL8188.843.827.014.54.81.43.511.721.753.93.65.270.23,5482,1911,178386112283238
Clifford RayClifford Ray1973-74CHICHI8089.332.99.312.23.10.72.23.97.751.11.52.560.82,63274797724658173281
Bobby JonesBobby Jones1976-77DENDEN8289.929.515.18.33.22.32.06.110.757.02.94.071.72,4191,238678264186162238
Kareem Abdul-JabbarKareem Abdul-Jabbar1975-76LALLAL8290.041.227.716.95.01.54.111.121.152.95.57.870.33,3792,2751,383413119338292
Ben WallaceBen Wallace2002-03DETDET7390.039.46.915.41.61.43.21.22.96.048.10.00.116.71.22.645.02,8735061,12612010423088179+222
Dave CowensDave Cowens1973-74BOSBOS8090.441.919.015.74.41.21.38.118.443.72.93.483.23,3521,5181,25735495101294
Nate ThurmondNate Thurmond1974-75CHICHI8090.534.57.911.34.10.62.43.18.636.41.72.858.92,75663290432846195271
Marcus CambyMarcus Camby2000-01NYKNYK6390.533.812.011.50.81.02.21.04.89.252.40.00.112.52.43.666.72,127759723526613663205+67
Dave CowensDave Cowens1974-75BOSBOS6590.740.520.414.74.61.31.18.818.447.52.93.878.32,6321,3299582968773243
Curtis PerryCurtis Perry1973-74MILMIL8191.029.59.08.72.31.31.24.09.044.61.01.758.22,38672870318310497301
Elvin HayesElvin Hayes1975-76WASWAS8091.137.219.811.01.51.32.58.117.347.03.65.762.82,9751,585878121104202293
Patrick EwingPatrick Ewing1998-99NYKNYK3891.234.217.39.91.10.82.62.66.514.943.50.00.10.04.36.170.61,300657377433010099105+47
Bill WaltonBill Walton1976-77PORPOR6591.334.818.614.43.81.03.27.614.352.83.55.069.72,2641,21093424566211174
Sam LaceySam Lacey1974-75KCOKCO8191.541.711.514.25.31.72.14.811.342.71.82.475.43,3789281,149428139168274
Kevin GarnettKevin Garnett2003-04MINMIN8291.539.424.213.95.01.52.22.69.819.649.90.10.525.64.55.779.13,2311,9871,139409120178212202+614
Tim DuncanTim Duncan1998-99SASSAS5091.539.321.711.42.40.92.52.98.416.949.50.00.114.34.97.269.01,9631,08457112145126146147+371
Elmore SmithElmore Smith1973-74LALLAL8191.636.112.511.21.90.94.95.411.745.71.83.159.02,9221,01590615071393309
Jerry SloanJerry Sloan1974-75CHICHI7891.633.012.26.92.12.20.24.911.143.92.53.374.82,57795353816117117265
StatMuse has season-level data for defensive rating going back to the 1973-74 season.