Matt Niskanen, late of the Pittsburgh Penguins, is one of the marquee defensemen expected to go to free agency tomorrow. New Caps beat writer Alex Prewitt covered the buzz around Niskanen in the Post this morning.

A move to Washington would keep Niskanen with his old defensive coach, Todd Reirden, who coached the blueliner in Pittsburgh and can speak knowledgeably about the player to the Caps front office. And at a glance, Niskanen looks like a very strong player.

Let’s check out ExtraSkater.com, which is the best site on the internet next to the Benedict Cumberbatch Name Generator. Last year with Pittsburgh, Niskanen saw 53.4 percent of shot attempts belong to his team during 5v5– a number 7.3 percent better than when he was off the ice. In 2012-13, he had a 51.2 percent shot-attempt percentage, a 3.6 percent improvement compared to when he was on the bench.

That looks fantastic, but hold on a second.

Possession is important. It’s probably the most important thing, but no one considers corsi scores to be the end of the conversation– rather just the opposite. The whole point of my statistical snapshot series last season was to use the numbers as a jumping-off point to discover why some things work and others didn’t. No understanding of hockey is complete without some kind of quantification of shot attempts, but quantification alone is not complete either. That’s why stat geeks look at a lot of different stuff in concert. Linemates, finishing ability, zone starts, team tactics, injuries, and even the “jokes” factor are all vital to knowledge.

For Niskanen, let’s take a look at how he performed when on the ice with different players over the last two seasons. Hockey Analysis does a great job packaging this up. I’ll limit it to skaters who spent more than 300 minutes with him. The first column shows the 5v5 shot-attempt percentage when the players are together. The second column shows what Niskanen does away from that player. The final column is the difference.

Pittsburgh was a notoriously top-heavy team last season, and Niskanen kinda shows that. When playing with dynamos like Crosby, he’s great. When he’s not, he’s mediocre. This isn’t a very sophisticated analysis, but these numbers suggest Niskanen is not actually driving possession and is just a passenger on an unbalanced team.

It’d be a mistake to sign Niskanen. And it’d be a huge mistake to sign Niskanen to the seven-year contract his agent bragged he could get for his client. If whoever ends up signing him expects Niskanen to perform just as he did backing up Sidney Crosby, they will be sorely disappointed. Considering how massive his payday is likely to be, it might end in a buyout.

Maybe it’ll be like Mike Ribeiro, who had good enough surface stats and tangible details to get a mondo contract from Don Maloney in Arizona, before getting promptly bought out once everyone (else) realized he’s just a passenger who looked good only because he was on a power play with Alex Ovechkin for 48 games. Ribs made $5 million last season, paid by a general manager who said, “we haven’t had resources to pay attention to the advanced stats.”

If only he had allocated some resources, Maloney would have saved his club $11.7 million— plus the $5 million they paid him last season. I hope the Caps can avoid a similar mistake. By digging just a little deeper than the basic stats– and it’s about time we consider possession scores to be basic– the Caps will recognize that Niskanen– like Ribeiro– is just a passenger.

UPDATE: Tyler Dellow recommended I compare Niskanen’s WOWY numbers to Brooks Orpik‘s.

Orpik fares even poorer than Niskanen. He doesn’t soar nearly as high with the best players, but he doesn’t drop as hard when separated from them. One thing I’d like to point out: despite my argument above that a corsi shouldn’t be the end of the conversation, a free agent defender who can’t muster above a 50.6 when skating with Crosby probably doesn’t deserve more evaluation.