This is by far the easiest and sure fire way to get rebounds, though i did use 2 controllers but you can do this against AI.
Firstly as you will have already done you want the
user sliders set to max (Bar injuries) and the
CPU sliders to minimum.
At the same time go into the
NBA Rules menu and turn the following OFF:
Shot Clock
Out Of Bounds
Backcourt
8sec Half Court
3 In The Key
5sec Back To Basket
Now with these rules off pick the player you want to get your 20 rebounds with and get possession of the ball (Getting your steals here would be a good idea so that you can achievement the
Get A Triple-Double in NBA 2K6 achievement).
With possession of the ball run (
) into you half of the court and behind
your net making sure to stand in front of the pole for your basket, press the
button to shoot which 99% of the time will hit the back of the basket and land near you,
this counts as a rebound even though it is off your own net. Now run to the opponents net stand in the 3 point zone (Outside the red line) and hold
to shoot (With the sliders all the way up you will always score)
Repeat this 20 times with the same player and you will have you 20 rebounds.
(And 60 points with one player, 20 steals with one player, 20 3-pointers scored with one player, all of which will all but complete the game for you, all that will be left is to score 140 points in the game to complete it)
You can check the stats by pausing, going into Game Stats - Home Team.
Here's a video showing the method.