Adding Aldridge makes the Spurs top contenders

— -- Did you feel a jolt this afternoon? A nation's celebration of Independence Day was interrupted by a seismic shift in the NBA when former Portland Trail Blazers forward LaMarcus Aldridge tweeted that he has agreed to sign with the San Antonio Spurs as an unrestricted free agent next week when teams can begin signing players after the league's moratorium period concludes.

This is the score in free agency the Spurs have dreamed of since their elimination from this past spring's playoffs at the hands of the Los Angeles Clippers. And presuming San Antonio is able to bring back Tim Duncan and Manu Ginobili at below-market contracts, it sets up the Spurs as the biggest threats to the Golden State Warriors in the Western Conference and possibly even co-favorites with the defending champs.

How San Antonio landed Aldridge

The Spurs started planning for today last fall, when they chose not to extend the contract of forward Kawhi Leonard. San Antonio took some risk that Leonard might look for a shorter offer sheet as a restricted free agent, but the trust built by the organization convinced Leonard to hang tight. That allowed the Spurs to head into this summer with Leonard's small cap hold ($7.2 million) on the books rather than the starting salary of the five-year maximum extension he agreed to Wednesday (still yet to be determined, but somewhere around $16 million).

San Antonio also took advantage of a small cap hold for wing Danny Green ($7.6 million), who also agreed to a new contract (four years, $45 million) that he won't sign until after the Spurs sign Aldridge. Trading Tiago Splitter's $8.5 million cleared more room under the cap.

The last step of the process has yet to be completed. To have enough space to give Aldridge the maximum salary, San Antonio also will need to re-sign Duncan and Ginobili to contracts smaller than their cap holds or renounce their rights. Presumably, Duncan -- who announced earlier this week that he will return for a 19th NBA season -- will sign for the remainder of the Spurs' cap space (somewhere between $5 million and $7 million, depending where the cap is eventually set). That would allow San Antonio to use its $2.8 million room exception to re-sign Ginobili, should he also opt against retirement.

That's a lot of sacrifice by the Spurs' players. The results might justify the salary they gave up.

How Aldridge fits San Antonio

Remember, despite the opening-round exit, San Antonio was starting with one of the best rosters in the NBA. The Spurs went 21-8 after the All-Star break, a 59-win pace, with a better point differential over that span (plus-10.3 points per game) than the Warriors managed during the regular season (plus-10.0). San Antonio's starting lineup outscored opponents by 23.6 points per 100 possessions, better than any other group that played at least 250 minutes, per NBA.com/Stats. And now the Spurs have gotten more talented.

Getting Aldridge will likely mean sacrificing some of San Antonio's trademark depth. Splitter is gone, as are backups Aron Baynes and Marco Belinelli (who signed with the Detroit Pistons and Sacramento Kings, respectively). The Spurs will have to renounce the rights to their remaining free agents, most notably promising young point guard Cory Joseph, and if Duncan and Ginobili return San Antonio will be able to fill out its roster only with players making the minimum salary.

Yet adding Aldridge was unquestionably worth it. His addition to Leonard and Duncan gives the Spurs the NBA's best frontcourt. Aldridge (second team) and Duncan (third) were both All-NBA selections last season, and Leonard received the most votes of any player who was not chosen All-NBA.

There will be something of an adjustment for Aldridge in terms of style of play. He's slotting into the starting lineup in place of players such as Splitter (18.5 percent) and Boris Diaw (18.4 percent), who used plays at a below-average rate. Aldridge's 30.4 percent usage rate ranked ninth in the league and was far higher than any San Antonio player ( Tony Parker led the Spurs at 24.6 percent). He won't be able to hold the ball and survey the court as much as he did in Portland.

Having another skilled offensive player has benefits for the Spurs, however. Playing through Aldridge in the post at times means relying less on Parker, the team's least efficient scorer. Aldridge can take on a leading role with San Antonio's bench units, given how much Duncan usually rests, and his own efficiency should be bolstered by playing against fewer double-teams. There's a gravity benefit too. The Blazers have been far better offensively with Aldridge on the court despite his own below-average efficiency because of the respect he commands as a midrange shooter.

Projecting the Spurs

Essentially, adding Aldridge should allow the Spurs to perform like they did after the All-Star break over a full season, something that would have been difficult otherwise because of aging and injuries. A projection based on a predictive version of ESPN's real plus-minus adjusted for age, using similar playing time to last season (with Aldridge's minutes per game dropping from 35.4 to 34 in San Antonio, which still might be optimistic), shows the Spurs with an offense 4.6 points per 100 possessions better than league average and a defense 6.0 points better. Those would have ranked San Antonio fifth in offensive rating in 2014-15, just behind the Cleveland Cavaliers, and first by a wide margin defensively.

The Spurs' 10.6 net rating per 100 possessions is not far off what Golden State managed last season (plus-11.5), and indeed this projection shows San Antonio winning an average of between 66 and 67 games, similar to last season's Warriors.

More frightening yet for West opponents, I'm still projecting the Spurs with replacement-level players filling out the bench. San Antonio could be even better if the team can convince veterans like former Indiana Pacers forward David West to sign on for the veteran's minimum in hopes of winning a championship.