After having watched the Thunder a dozen or so games in the last month, I've come to notice that their entire rebounding scheme is designed around boxing out bigs and letting Westbrook crash the glass uncontested. This isn't to say Westbrook isn't a great rebounder relative to his position, because he's one the best, but his rebounds are absolutely inflated.
Westbrook is leading the NBA in uncontested DREB's with 7.9 rpg, even higher than guys that are anchored around the rim for defensive purposes like Whiteside, Gobert, Jordan, and David.
http://stats.nba.com/players/defens...GE*5&Season=2016-17&SeasonType=Regular Season
Beyond that, Westbrook has BY FAR the lowest contested DREB% in the league for any player averaging >5 RPG.
http://stats.nba.com/players/defens...GE*5&Season=2016-17&SeasonType=Regular Season
One might start to wonder how a PG could be accumulating so many uncontested rebounds, digging into Westbrook's shot contests gives a clearer picture
http://stats.nba.com/players/hustle...D=1610612760&CF=PLAYER_NAME*E*&PerMode=Totals
Westbrook has contested a grand total of 160 FG's on the ENTIRE SEASON.
That number is staggeringly low and to be frank, flat out embarrassing. To put his 3.4 contests per game in perspective, OKC backup PG Cameron Payne is averaging 4.1 contests per game while playing in less than half of the minutes that Westbrook is.
Westbrook ranks dead last in the NBA in contested shots among players averaging 30 or more MPG by a considerable margin. Hilariously, the only two players who have contested less 3P FGA's are Rudy Gobert and Whiteside, who have contested 53 and 64 respectively. Russell Westbrook is at 69 while having playing close to the same amount of minutes...Yes, DeAndre Jordan has contested more 3P FGA's this season than Russell Westbrook.
http://stats.nba.com/players/hustle...=Regular Season&CF=MIN*GE*1400&PerMode=Totals
Some people may point to other names on that list, i.e. Jimmy Butler, showing they have fairly lower contest numbers as well. The difference being Jimmy Butler's counterpart is attempting 4 fewer FGA than Westbrook's.
Westbrook is contesting approximately 3.4 of his PG matchup's 13.1 FGA while on the floor. The player he's supposed to be defending is attempting 74% of their shots without a contest from Westbrook. Butler on the other hand is right around 45%.
http://www.82games.com/1617/16OKC1.HTM
Ignoring the fact that he leaving his man with regularity to chase rebounds, even when Westbrook contests shots he's the worst guard in the league in expected FG% against.
His opp. +6.9% over expected FG% is dead last in the NBA among guards. The only other players over 4.5% are Sean Kilpatrick, Kyle Korver, and Emmanuel Mudiay.
http://stats.nba.com/players/defens...rMode=Totals&CF=D_FGA*GE*300&PlayerPosition=G
Back to Westbrook's raw rebounding numbers. Beyond his absurd REB rate on uncontested FGA, Westbrook is averaging an absurd 1.2 uncontested DRPG on missed FT's. All of the top rebounding bigs in the league are between 0.4-0.7 per game, Westbrook is doubling their frequency while operating out of 3 position.
Rather than operate under the typical box out on opponent FT's, OKC is instead placing Westbrook in the 3 position and pinching the opponent FT rebounders, forming a triangle which allows Westbrook to slide into position and "steal" rebounds. While this technique is often employees when a team has a decisive front court disadvantage, the Thunder implement it all times with Westbrook on the floor despite featuring two 7 footers who are elite rebounders in their own right. This has enabled Westbrook to further add to his rebounding numbers, almost doubling the next highest uncontested FTREB in the league.
One might ask why this matters? It essentially opens the paint offensive rebounds on missed FT's to anyone that isn't operating in the 4 or 5 position. As a result, OKC is actually 2nd worst in the NBA in FT defensive rebounding.
http://stats.nba.com/player/#!/201566/rebounds-dash/
Here is a video clip from fansided demonstrating the technique
https://mtc.cdn.vine.co/r/videos/28...p4?versionId=GL_iej_GnMNDV.kkj5xrZXvwFiaVGklr
Finally, and probably the most damning statistic, is that 7.0 of Westbrook's 10.4 rebounds per game are coming on missed FGA from 13+ feet. The largest proportion of those, 4.2, are from 19+ feet. That number ranks 4th in the NBA behind only Whiteside, Jordan, and Drummond. 83% of those rebounds on misses from 19+ feet are uncontested rebounds, meaning Westbrook had 0 competition for the board.
Why is a point guard able to grab rebounds on missed long shots without contest so frequently? Why is he not guarding the opposing point guard when there's a FGA so far away from the basket? The opposing PG obviously isn't in the paint next to Westbrook, or the rebound wouldn't be uncontested. Is he just abandoning his man when a player has the ball on the perimeter and is likely to shoot?
Summary: Westbrook is almost never contesting shots, instead he's leaving his man open and blatantly attacking the paint in search of defensive rebounds with a numbers advantage. Beyond this, the entire rebounding culture of the team has been centered around the bigs boxing out and deferring rebounds to Westbrook. Additionally, due to his position being perimeter oriented, his constant search of rebounds has compromised OKC's perimeter defense, which ranks dead last in the NBA in opp. guards expected FG% by a considerable margin.
EDIT: let me add some additional things that are frequently being asked/used to criticize the data
I've seen many reference OKC's transition offense as a reasoning for scheming around Westbrook rebounds. OKC ranks 13th in the NBA in transition offense and averages around 17 fast break points per game, ~4 higher than league average. Given their overall offensive ranking of 16th overall, transition offense actually has little overall effect on their team efficiency given it's responsible for less than 20% of their total offensive possessions.
After running the numbers, OKC would only average ~0.5 less PPG if they were completely average in transition(efficiency and volume).
OKC's slightly above league average with 27.0 uncon DREB. Factoring for variance and Westbrooks superior PG rebounding skills, he's grabbing right around 40% of all possible uncontested DRBS when on the court. OKC grabs 51.8% of all rebounds with Westbrook on the court. Without Westbrook, they're at 50.9%. That 0.9% drop is largely non-significant. Further more, last season OKC was the greatest rebounding team in NBA history +8.4/game. This season, they're still above average at +3.4, but nowhere near as dominant despite Westbrooks historic REB rate.
http://www.82games.com/1617/16OKC1.HTM#onoff
He's contesting 3.5 FGA per game, that's less than their backup PG and the worst in the league by a considerable margin for a player averaging>30 mpg.
http://stats.nba.com/players/hustle...016-17&SeasonType=Regular Season&CF=MIN*GE*30
He's contesting less than half of the shot attempts that he was last season(3.4 vs 7.4) and the ones that he is contesting, he's doing a terrible job, as he ranks dead last in the league in opponent expected FG%.
Westbrook's rebounding effect on W/L's has been overstated. They're 5-4 and allowing 108 ppg in games he's had >13 rebounds. Their opponents in that 9 game stretch are Golden State, Washington, Denver, Miami, New Orleans, New York, Detroit, Charlotte, and LA.
These are his opponents he's had >11 rebounds and OKC won. @T Wolves, Suns, @ Kings, @ Kings, @ Celtics, Pelicans, @ 76ers, Celtics, Magic, Grizzlies, @ Hawks, Suns, @ Pistons, @ Knicks, Pelicans, Heat, and Nuggets.
These are his opponents that he's had >11 rebounds and OKC lost: Warriors, Hawks, Pacers, Clippers, Hornets, Wizards, Pistons, @ Kings, @ Twolves.
In addition to being terrible at contesting shots, he's also dead last in the league in opponent drives
http://stats.nba.com/players/defens...E_NUM&dir=1&CF=FGA_LT_06*GE*75&PerMode=Totals
His opponents are driving on him with the 4th highest frequency while shooting 10.8% above average when guarded by Westbrook.
He's dead last in the NBA in contested shots in a position that leads the league in FGA. Westbrook's allowing his opponent 4.6 wide open(not within 6 feet) shots per game, which is 1.8 FGA higher than any other player in the league.
The only 2 players averaging >30 minutes per game and contested less 3PA are Gobert & Whiteside.
In contrast with last season, overall, defenders are shooting 6% higher from the field, 2% higher from 3, 10% higher from 2, and 9% higher inside 10 feet this season vs Westbrook than they did in 2016.
2nd Edit: Those referencing Westbrook's rebounding in wins and losses.
Here are the teams they've beaten when he gets 10+ boards
Atlanta
Boston X 2, one was without I. Thomas
Brooklyn
Denver X 2, both without Jokic
Detroit
LA Clippers without CP3 and Griffin
LA Lakers
Memphis
Miami without Dragic
New Orleans X 3
New York
Philly the 2nd game of the season
Phoenix X 2
Sacramento
Utah
Washington when they were 6-11
http://bkref.com/tiny/2Xn82
Additionally, Westbrook played 34 or more minutes in all but one of those games, against the Clippers Meanwhile OKC has lost a total of 9 games where Westbrook failed to record 10 rebounds. The minutes played in those games were as follows
L 80-114 Memphis 23 minutes 5 rebounds, Memphis shot 53% from the field
L 95-114 Portland 27 minutes 6 rebounds, Portland shot 54% from the field
L 96-122 @ Golden State 29 minutes 6 rebounds, Warriors shot 52% from the field
L 98-120 @ LAC 29 minutes 5 rebounds, Clippers shot 55% from the field
L 89-109 @ Utah 30 minutes 5 rebounds, Jazz shot 58% from the field
L 94-98 @ Milwaukee 35 minutes 7 rebounds, Bucks shot 48% from the field
L 109-111 @ LA Lakers 35 minutes 8 rebounds, Lakers shot 51% from the field
L 116-118 @ Houston 37 minutes 8 rebounds, Rockets shot 48% from the field
L 112-102 Toronto 38 minutes 7 rebounds, Raptors shot 52% from the field
His poor rebounding in losses isn't the causation, rather it's the other team shooting a much higher percentage from the field thus reducing rebound opportunities and Westbrooks minutes due to the games being blowouts.
Edit 3: Westbrooks increase in rebounding over the past 4 seasons
After looking into his numbers, the only difference between Westbrooks rebounding numbers from 2013-present has been his uncontested defensive rebounds.
#2013-14
Westbrook averaged 5.7 rpg
3.7 of those rebounds were uncontested DREBs
http://stats.nba.com/player/#!/201566/rebounds-dash/?Season=2013-14&SeasonType=Regular Season
#2014-15
Westbrook increased his average to 7.3 rpg, 1.6 more than 2014
4.5 of those rebounds were uncontested DREBS, an increase of 0.8
Kevin Durant was injured for the majority of this season. OKC was forced to play with 2 SG's in place of a SF which likely led to Westbrook's career high in ORB.
#2015-16
Westbrook increased his average to 7.8, 2.1 more than 2014
6.0 of those rebounds were uncontested DREBs, an increase of 2.3 from 2014
#2016-17
Westbrook increased his average to 10.7 rpg, 5.0 more than 2014
7.9 of those rebounds were uncontested DREBS, an increase of 4.2 over 2014
So he's rebounding at roughly the same rate in all areas over the past 4 seasons sans uncontested defensive rebounds, where he's greatly increased his production and his overall rebounding has scaled almost linearly.
.His backup averages more contests than he does in half the the minutes. DeAndre Jordan has contested more 3 pt shots than Russ. In fact the only two other players in the NBA who play 30+ minutes and have less 3pt contests are Gobert and Whiteside. His opponents are shooting 11% when guarded by him. He is giving up 4.6 wide open shots beyond 6 ft. Nobody else in the entire NBA is even giving up 3 such shots A game. 
