Depending on whom you ask, Tom Landry either revolutionized or invented the 4-3 front. When he became head coach of the expansion Cowboys, Landry’s teams always fielded four down linemen. And by the time he was forced out, the 3-4 fad that dominated the ’80s had subsided, resulting in Dallas running a 4-3 front every season from 1960 to 2004.

In 2005, several key changes happened in Dallas. Bill Parcells was hired as head coach in ’03, but he didn’t implement a scheme shift right way. After Dallas ranked 27th in points allowed in ’04, though, changes were necessary. With two first round picks, the Cowboys selected 3-4 outside linebacker DeMarcus Ware and 3-4 defensive end Marcus Spears. Dallas also signed Jason Ferguson, who had played nose tackle for Parcells with the Jets. With the pieces in place, Dallas ran a 3-4 defense each of the last eight seasons. Ware has become one of, if not the, greatest 3-4 outside linebackers of all time. But after eight years of Parcells, Wade Phillips, and Rob Ryan, Dallas is returning to its 4-3 roots under Monte Kiffin.

Kiffin, of course, is most famous for the outstanding defenses that he and Tony Dungy created in Tampa Bay; the Tampa-2, after all, has became part of football nomenclature. But I don’t want to go into whether the Cowboys are well-positioned to switch fronts (they’re not) or who will play what role in 2013 (Ware and Anthony Spencer are moving to defensive end, Jay Ratliff will move from NT to DT, and newly rich Sean Lee will play as a true middle linebacker, and he might be even more valuable in this system). Instead, I want to take a 30,000 foot view.

In 1974, the 3-4 defense was introduced to the NFL by Bum Phillips in Houston, Lou Saban in Buffalo, and Chuck Fairbanks and Hank Bullough in New England. I thought it would be interesting to see how teams that switched fronts fared in their first season. On caveat: I wanted to exclude schizophrenic teams like the current Bills (4-3 defense in 2009, 3-4 in 2010, 4-3 in 2011 and 2012, and now a 3-4 again in 2013).  According to my records, 74 teams in NFL history have switched from a 4-3 to a 3-4, or vice versa, after running the same front for the three prior years.
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