The Great NBA Coaching Purge has gotten so bad that six teams made changes the first seven weeks of the season; 14 have had a switch since the end of last season; Erik Spoelstra took over in Miami in the summer and already is tied for 17th in tenure; and Mike Woodson, in his fifth season in Atlanta, has the longest active run in the Southeast Division by four seasons.

It has gotten so bad that Monday, the day Reggie Theus got fired, coach Kevin McHale stood inside Arco Arena a few hours before his Timberwolves faced the Kings and joked that he was a few weeks from catching up to 20-year-man Jerry Sloan on the longevity list.

McHale had been on the job seven days.

It’s that kind of gallows-humor world for coaches these days. One team short of half the league has undergone a sideline transformation since the end of last season, and the six already in 2008-09 doubles the previous pre-Christmas record.

“Yeah,” Magic coach Stan Van Gundy told the San Francisco Chronicle, “it’s more than a little stunning.

“Once it starts, it’s easier for the next guy because it doesn’t seem so ridiculous to fire your coach early in the season because somebody else did it. Now five other teams have just sort of jumped on the bandwagon.”

So that’s one explanation. Momentum.

What about defense? Offense has always been more about skill and defense more about focused effort. It’s not an umbrella explanation — a roster with mostly players who can’t or don’t defend will not be good on defense, period, as the Kings have found — but coaches regularly take the fall when their charges have that yawning look.

The Kings, Timberwolves, Thunder, 76ers, Raptors and Wizards have done the firing. As of Monday, the day Theus joined the ever-expanding list, they were 28th, 26th, 29th, 14th, 20th and 30th, respectively, in shooting defense, the best barometer of stopping the ball. Maurice Cheeks in Philadelphia paid more for having one of the league’s worst offenses despite the presence of Elton Brand, Andre Iguodala and Andre Miller and a losing record amid expectations of a long playoff run.

Said expectations? It’s not the major cause this season, at least not so far.

Cheeks with the 76ers and Sam Mitchell with the Raptors have been the only real victims of preseason hype. Eddie Jordan got it in Washington with the Wizards flailing away, but they could only have realistically expected to be passable until Gilbert Arenas returns from injury, not among the Eastern Conference leaders.

The three others were on a fast track to the lottery after being routinely projected for the lottery: the Kings, Thunder and Timberwolves. Oklahoma City has been the worst team in the league, just as most predicted. The case easily could be made, though, that the Kings and Thunder, in particular, were underachieving even in that light.

Players ruling the world? They know when a coach is vulnerable, and they know they can do something about it, one way or another. Play hard, he often stays. Roll over, he often goes.

“Players know when a coach is in trouble whether they want to play or they don’t have to play, and their agents know what’s going on,” said Sloan, who recently marked his 20th anniversary as coach of the Jazz. “When that happens, it’s pretty difficult to pull out of, unless you have the support.”