Just when you thought it was safe to go back in the water, it’s open season on NBA coaches.

In the past week alone, Cleveland’s Paul Silas, Dallas’s Don Nelson, and Orlando’s Johnny Davis all exited the stage. With only a month left in the season, it’s odd that even one team would change captains, let alone three.

Normally, the coaching reaper appears between December and the All-Star break, taking most of his victims during this period. Then the coaching landscape quiets down in March since everyone else is content to wait until after the season. But as we’ll see, two of the three late movers had sound logic behind their decisions.

Let’s start with the only one of the three that was voluntary, which was Nelson and his decision to retire from Dallas. The Mavericks did something very rare in the world of sports – they had a succession strategy. Dallas had slowly groomed Avery Johnson to take over for Nelson during the course of the season. He had been running the team’s practices and took over the team for several games while Nelson dealt with a few health issues.

As a result, this was just a case of Nellie opting to leave sooner rather than later. At 64, he undoubtedly realized he’d lost a little bit of his fire, and there was a decent chance that owner Mark Cuban would have made him walk the plank after the season anyway unless Dallas won the title.

Interestingly, the Mavericks play a different style under Johnson, but with nearly the same level of effectiveness. The team’s victory margin under Johnson is slightly better – 5.3 to 4.4 – but that’s only because his last two games were against bottom-feeders Charlotte and New Orleans. However, the Mavs have been much more defense-oriented with Johnson at the helm, both scoring and giving up about five fewer points a game under the Little General.

As a way of driving home his attention to defense, Johnson yanked Jason Terry not once but twice in the New Orleans game after the guard missed defensive assignments, bringing a new accountability to the Mavs at that end of the floor.

At the same time, Johnson has committed more strongly to Terry as the starter at point guard, a marked contrast to Nellie’s interminable fidgeting at that spot. Johnson doesn’t have Nelson’s offensive genius, so he’ll need to make up for it by coaxing a greater effort on defense and using his personnel more wisely. So far, so good: The Mavs are 11-4 when Johnson is on the bench.

Then we have the case of Silas, who in theory was axed because the Cavaliers went 4-9 following the All-Star break after spending much of the season’s first half atop the Central division. In reality, new owner Dan Gilbert has had an itchy trigger finger ever since his purchase of the team was approved last month.

Gilbert knows he has two years to convince LeBron James that the Cavs are a world-class organization, or he risks losing LeBron as a free agent to New York or Los Angeles. James’s endorsement contracts have major kickers if he goes to either of those cities, so there’s a strong incentive for him to bolt unless the situation in Cleveland improves.

A major part of Gilbert’s plan to keep James is to woo Phil Jackson or Cleveland native Flip Saunders to take over the team this summer, which obviously is much easier with Silas out of the picture. While he’s at it, Gilbert may also send general manager Jim Paxson packing. Although Paxson fleeced the Magic in the Drew Gooden trade, he’s authored several other questionable maneuvers that have left LeBron with little help. That was plainly apparent in Sunday’s loss to Toronto when the Chosen One scored 56 points, Gooden chipped in 24, and the rest of the team mustered just 18.

In that game, Silas finished digging the grave that Gilbert had started for him. Upset with his point guard play, Silas benched usual starter Jeff McInnis and started Eric Snow. After the game (but before he was fired), Silas said he thought the switch went well; it would have gone better had Snow scored a point. His 40 scoreless minutes were the main reason Cleveland lost despite LeBron’s heroics.

With a perfect reason landing on his doorstep, Gilbert followed through on a choice he’d made a long time ago. While it’s true that Silas had other black marks on his record (run-ins with Eric Snow and Ira Newble and a strange unwillingness to use Jiri Welsch and Anderson Varejao), those wouldn’t have been fireable offenses if not for the big picture of Gilbert going for a higher profile coach.

That contrasts with Orlando’s decision to ax Johnny Davis, which had “knee-jerk reaction” written all over it. I’ve never been a huge fan of Davis because I think he runs too loose a ship, but it’s difficult to see how firing him now benefits the Magic in either the short or long term. It’s not like there was a capable replacement waiting – Orlando GM Jon Weisbrod turned the team over to somebody named Chris Jent of Sparta, New Jersey. Jent was so far down the coaching depth chart that he didn’t even sit on the bench during games – he had to sit behind it.

Now, out of the blue, Jent is in charge of Orlando’s playoff push and has to get the respect of a recalcitrant pupil, guard Steve Francis. In a related story, Orlando dropped behind Philadelphia in the race for the eighth and final playoff spot with Monday’s loss to the Bobcats.

Orlando’s decision to replace Davis was the result of a slide that was the GM’s making, not the coach’s. The Magic’s second-half decline began when Weisbrod traded Cuttino Mobley to Sacramento for Doug Christie, who is now out for the season with foot problems. Orlando was 18-14 at the time of the deal, and 14-21 since. Pinning that on the coach is a transparently disingenuous CYA maneuver on Weisbrod’s part.

So while it’s at first puzzling that three teams would swap coaches so late in the season, only Orlando’s move is a true head-scratcher. Not surprisingly, Dallas and Cleveland will be playing in the postseason, while Orlando’s sacking of Davis, designed to prod its playoff run, probably will have the opposite effect.

In the big picture, however, this week’s coaching turnovers are yet another sign of the times. Never in history have pro basketball coaches enjoyed less job security. Every team in the East has changed coaches in the past two years, as have all but four teams out West.

Granted, getting fired is an inevitable part of coaching because once the players tune a guy out, the only recourse is to bring in somebody new. But the rate of change in the past two seasons amounts to more than culling a few coaches whose messages had grown stale. It speaks to a growing impatience and short-term focus on the part of general managers (most of whom are oddly secure in their own jobs, by the way), of which Weisbrod’s rash dismissal of Davis is a perfect example.

Blame it on talk radio or increasing fan scrutiny, but GMs increasingly feel the need to save face when their moves don’t pay immediate dividends. In these bloodied waters, no coach can feel safe.