Most new NFL head coaches are given four- or five-year contracts. Few make it to Year 4.

On Monday, two first-time head coaches were fired after the third season, while all signs point to the Colts making it a trifecta at some point soon.

Raheem Morris is out in Tampa, Steve Spagnuolo is out in St. Louis, and Jim Caldwell is expected to be out in Indianapolis. During the season, Todd Haley was given a pink slip before he was even able to complete his third year in Kansas City.

Because they’re usually taking over bad, rebuilding teams, new coaches are usually given a two-year grace period. After that, there’s no excuse for a lack of success in a league where anyone can go from zero to hero in a 730-day span.

And while Caldwell is a special case after relieving Tony Dungy for the then-contending Colts, the career arcs of Morris and Spagnuolo are remarkably similar.

Both struggled to revive struggling franchises in 2009, winning a grand total of four games out of 32. Both rebounded with overachieving years in 2010, making playoff runs in the NFC and combining to go 17-15. During those first two seasons, they drafted supposed franchise quarterbacks — Josh Freeman in Tampa Bay, Sam Bradford in St. Louis — both of whom were expected to flourish in 2011.

That didn’t happen in either case.

Spagnuolo finished his three-year run on a seven-game losing streak that saw his team get outscored by an average of 13.4 points per game. Morris went out on a 10-game losing streak, in which his Bucs were outscored by 16.5 points per game. There were definitely questions about whether the Rams gave up on Spags. With Morris, there was little doubt.

In the end, they went 6-26 in Year 3, which shows some serious regression.

Maybe it was bad timing. Had you switched the results from 2010 with the results from 2011, both might have survived this offseason. Instead, they were bitten by the third-year curse.

The major difference, of course, is that Morris was one of the youngest head coaches in NFL history, which also appears to be a curse. And double whammy curses are the worst kinds of curses. Morris joins the likes of Josh McDaniels, Lane Kiffin, Eric Mangini and Dave Shula as a failed first-time head coach hired before the age of 35.

This doesn’t mean that the future isn’t still bright for the 35-year-old Morris and the 52-year-old Spags. Both will likely land positional or coordinator jobs elsewhere, and I wouldn’t be surprised to see either emerge as head-coaching candidates in the years to come. The worry, right now, is that two coaches with defensive backgrounds failed largely because of their defenses, both finishing in the bottom 10 in points allowed (Morris’ Bucs finished dead last).

As for Caldwell, I’d say the chips were stacked against him in 2011. There was the whole Peyton Manning thing, and then there was…well that’s all you need to know. I’m not sure it’s fair to fire him considering the circumstances this year, but then again I’ve never been convinced he’s a very good head coach.

Whoever replaces Morris, Spags and Caldwell (if indeed he gets fired) will have top-five draft picks in 2012. The expectations will be low at first, especially in St. Louis, but the clock will seem to tick faster as the losses mount, and there’s a solid chance we’re discussing new job openings in St. Louis, Tampa and Indy three years from now.