The Knicks are legit. If they can keep this up is another question.

The Knicks are 6-0, the last undefeated team in the NBA — and it’s not a fluke.

They are defending better than anyone in the league, giving up just 93.6 points per 100 possessions, via Hoopdata. (Anyone who says they just started defending this year wasn’t watching last year.) Their offense with Carmelo Anthony at the four is clicking, they are averaging 111.3 points per 100 possessions, again best in the NBA. Raymond Felton back at the point has steadied the decision making and added points.

If you questioned their competition, they just knocked off the Spurs in San Antonio. They are moving the ball on offense; their defensive rotations and hustle are sharp for this time of the season.

They are legitimate…

Well, let’s define legitimate. We are 7.3 percent of the way into their regular season. When we look at an East where the 76ers are without Andrew Bynum and the Celtics are struggling to find their groove, suddenly the idea of a top 3 or 4 seed and advancing out of the first round of the playoffs seem very legitimate.

But that’s not what Knicks fans are thinking… or at least starting to let themselves dream about.

And I’m far from sold on those big dreams. Because it’s a long season. Because of regression to the mean. And because there are some big hurdles ahead. (Oh, and because of the Miami Heat.)

First, the long season. Showing you can string together six good games — the first six, or six in January — only shows potential, not the ability to sustain a level of play. The Knicks will continue to be legit because they are defending, they are not going to fall off the map (baring major injury). But looking like a contender in November and in May are two very different things.

Second, regression to the mean — the Knicks are playing over their heads right now.

This season they are shooting 42.8 percent from three, a huge jump from the 33.6 percent of last season. J.R. Smith is shooting 73.7 percent from three through six games. That is not going to last. New York will be better from three than last year, but they are not going to keep hitting threes at this rate, and that is going to impact the rest of their offense when Jason Kidd is missing those threes in the fourth quarter, not burying them.

Generally, shots are just falling for the Knicks — they are hitting the highest percentage of spot-up jumpers in the league. They are getting 23.4 percent of their offense from spot-up shoots and they are hitting 45.1 percent of those shots (stats via Synergy Sports). That will slip.

Or, there is this note on twitter from Zach Lowe of Grantland: “Knicks have turned the ball over 9.9% of their possessions. Would be easily the lowest TO rate in league history. Uptick coming.”

Things are going to normalize for the Knicks.

And then they are going to have to integrate Amare Stoudemire back into the offense.

This really remains the question out there — the offense is clicking with Carmelo Anthony at the four, can you really start Stoudemire at the four and move Anthony back to the three again? Not and succeed at this pace. Right now the Knicks are getting 15.5 percent of their offense from isolation and they are shooting just 36.7 percent in isolation (13th in the NBA).

The Knicks are sharing the ball right now, they can’t go back to ‘Melo isolating on the wing 23 feet from the hoop. Not and win.

There’s a lot of potential with this Knicks team — Tyson Chandler has compared the makeup of this squad to the 2011 Dallas Mavericks title team. That’s lofty, and that team needed a Texas-sized load of things to go right for them to get the ring.

Things are not going to keep going this right for the Knicks, and when they don’t we’ll see what kind of team this really is.