Managing expectations of Pau Gasol's defense and rebounding

Any time a living legend retires, the team they leave behind is expected to struggle, especially when the legend was as productive as Tim Duncan was last season. Spurs fans have dreaded the post-Duncan future for years, because of the expected decline into irrelevancy.

Fortunately, the front office prepared ahead and had a core in place to keep San Antonio in the title hunt with Kawhi Leonard, LaMarcus Aldridge and a good supporting cast. Then, just as Duncan hung them up, they added Pau Gasol to the mix.

As we've covered, Pau doesn't address the team's flaws but is still a versatile player who should be an offensive upgrade over last season's version of Tim Duncan. Better yet, going by the few metrics often used as shorthand for good defense and rebounding, Gasol looks like a reasonable facsimile of Duncan as well, which understandably has fans giddy about the addition.

Unfortunately, Pau is quite a downgrade in those two areas, something that becomes painfully evident when going deeper into the numbers and the game tape.

There's more to defense than rim protection

When it comes to centers, one of the base skills required to be considered a good defender is at least adequate rim protection. Without it, it's extremely hard -- though not impossible -- to build a good defense. Having someone who can block or alter shots near the bucket takes away one of the most efficient areas of the court and the truly great rim protectors often allow their teammates to stay home on three-point shooters. It's a big part of the job.

But it's not the only part. There's a reason why Roy Hibbert has seen the league pass him by and why there were questions entering the offseason about Hassan Whiteside's bona fides as a defensive anchor despite his ridiculous block numbers and a very good defensive field percentage at the rim. The problem with those two players is the same we see with someone like Brook Lopez and ... Pau Gasol. They don't have the mobility to do anything other than stand close to the rim to bother shots.

That lack of quickness puts tremendous pressure on perimeter defenders, especially after pick and rolls. If they don't manage to navigate the screen and stay close to the ball handler, they are giving up either an open elbow jumper or a floater. When it comes to players with range that extends to the three-point line, things get even worse. The big man has to choose between stepping out while risking a blow-by, or staying in the paint and allowing an open pull-up. Sometimes even hanging way back isn't enough to prevent a drive.

Rim protection became a buzzword years ago, when most teams played at least one traditional big man and LeBron James and Dwyane Wade were dominating the league with the Heat by punishing opponents inside. Now that the game has become more perimeter-oriented, it still has value but it's not as important as being mobile enough to defend on the perimeter.

Despite good protection numbers, the immobility of centers like Whiteside, Lopez, Hibbert and Pau makes them liabilities in certain matchups and prevents them from being truly great defenders.

It's easy to overrate rebounders like Gasol

Pau ranked sixth in rebounds per game and seventh in defensive rebound percentage. By those numbers -- the ones most often used to get a sense of rebounding ability -- he's actually good on the boards. But a dive into other available stats paints a different picture.

Gasol ranked very low in defensive rebound chance percentage, a SportVU-powered metric that tracks the percentage of defensive rebounds within his vicinity that a player actually grabs. His percentage was very similar to Tim Duncan's, but Tim was significantly better at grabbing contested rebounds and he deferred to teammates on more uncontested boards than Gasol did. So in adjusted defensive rebound chance percentage -- a metric that excludes the rebounds that were deferred -- he ranked significantly higher than Pau. In fact, so did all the Spurs' rotation bigs, including Boris Diaw and David West.

This means that Pau seems to gobble up uncontested defensive rebounds which could have been collected by teammates and struggles to gather those that are contested. That's obviously not ideal, but what's even more worrisome is his effect on the glass at the team level.

Gasol has played center for the past three seasons. Before that, he shared the court with Andrew Bynum and Dwight Howard. In each of these seasons, his team has rebounded better on defense with him off the floor, significantly so in his two years as a Bull. All of those squads ranked in the bottom half of the league in defensive rebound percentage, which seems to suggest that it's hard to be good on the glass with Pau playing big minutes in the position he's best suited to occupy at this time in his career.

The reason why that happens is because Pau is not only mediocre when it comes to securing rebounds, but he also doesn't box out. That's evident when watching him play, as he relies on length to secure misses, which is understandable since he doesn't have the bulk or the strength of most full time centers. The numbers also back this up. By February of last season, Gasol had the second most missed blockouts in the league, according to tracking site Vantage Sports.

Pau's per game rebounding numbers make him seem elite, when in reality he's been closer to a drain on his teams.

Gasol is a limited defender and a mediocre rebounder, but he still can help

Every time there's a new high-profile addition to a team, the temptation is strong to look past obvious flaws or dismiss them as a product of a bad environment. That's what happened last season with David West and what happened in the past with Richard Jefferson and then Stephen Jackson. When it comes to a future first ballot Hall-of-Famer and all-around good guy like Pau Gasol, it's even easier to imagine a scenario in which everything works out for the best.

But it's unrealistic to expect a 36-year-old to magically go back to being among the best in the league in those areas -- especially when the player in question has been showing signs of decline as a defender and rebounder.

That doesn't mean it won't happen. Maybe Pau finds the motivation to grind on the boards and moves his feet on defense in San Antonio. Even if he doesn't, the Spurs were so good in both areas last season that they are uniquely prepared to sustain a dip while remaining among the best in the league.

It's hard to imagine the Spurs falling out of contention next year, which is quite a prospect after losing Duncan. Having Pau is one of the reasons for San Antonio's expected presence at the top of the standings.

That's a good enough reason to be happy he'll be wearing Silver and Black, despite his undeniable weaknesses.