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As he unwound in a hotel pool the next day, Winston had an epiphany: If entire teams could be rated and compared, then why not individual NBA players?

Winston ran the concept by Sagarin, a close friend since their days as fellow MIT undergraduate math majors. They settled on a variation of hockey’s plus-minus system, in which players are judged by how well their team plays while they are in the game.

In the NHL, for instance, a player who is on the ice when his team tallies a goal earns a rating of +1; if the team yields a score, that same player would receive a -1 mark.

“Basketball’s a team sport, and lots of things aren’t tracked,” Winston says. “Like taking the charge, going through a screen, tipping a ball to your teammate, saving a ball from going out of bounds. That’s where our system comes in. All these little things should translate into points.”

One problem: Traditional plus-minus systems tend to overrate average players on good teams and underrate good players on lousy ones. After all, a zero plus-minus rating on the Los Angeles Lakers is not the same as a zero rating on the Los Angeles Clippers, mostly because one team has Kobe Bryant and Shaquille O’Neal and the other has Marko Jaric and Chris Kaman.

To compensate, Winval’s ratings are weighted to take into account every other player on the floor. For every time segment a player is in a game, the system tracks the other nine players on the floor, the length of the segment and the score at the start and end of the segment.

The result of all that math? Rankings that sometimes refute conventional NBA wisdom. High-scoring players like Vince Carter, Dirk Nowitzki and likely MVP winner Kevin Garnett are among Winval’s top 10. But so is San Antonio’s Bruce Bowen, an unsung defensive specialist who averages just 6.8 points a game.

On offense, Bowen makes the defending league champs less than a point a game better than an average NBA player. On defense, however, the Spurs are 10 points a game stingier with Bowen on the floor.

Sacramento’s Brad Miller and Denver’s Nene fare well for similar reasons, while the Nuggets’ Anthony, the Kings’ Mike Bibby and New York’s Stephon Marbury rate lower than you might expect.

“Marbury’s one of the top 10 players on offense,” Winston says. “Everybody thinks this guy is a great player. But when he’s on defense, he gives it all back.”

Before every Dallas game, Winston and Sagarin sift through a 38,000-row spreadsheet of raw data, then send a customized scouting report to Mavericks assistant coach Brian Dameris. Each report contains a list of hot and cold players for each squad, drawn from individual Winval ratings over the previous five games.

Two weeks ago, for example, Golden State’s Mickael Pietrus ranked as the league’s third-hottest player; not coincidentally, the seldom-used rookie averaged 14.2 points and 30.3 minutes over a six-game stretch, far better than his season averages of 4.7 points and 13.3 minutes.

Had the Mavericks played the Warriors, the Mavericks would have known to give Pietrus extra defensive attention. Conversely, cold ratings can tip Dallas off to struggling or injured opponents.

A few years back, Winston couldn’t figure out why Jason Kidd’s normally stellar rating had taken an abrupt nosedive. It later came out the All-Star guard had been involved in a domestic altercation with his wife.

“DeShawn Stevenson, on Utah last year, his rating was really bad for two weeks,” Winston says. “The next week, I found out he was suspended from the team. So we can spot these guys having problems. We don’t know if they’re marital, psychological, injuries. But if a guy starts playing [bad], we know it. And the Mavs go at him.”

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