The crucial part to understand about front “spacing” is that it does not matter what front the defense starts in, only what front they end up in post snap. In the simplest term there is only one detail that differentiates a front from Odd and Even, and that is where is the run fit “bubble” or open gap. In even spacing the open gap is the B gap.

an ODD FRONT has an ODD number of down linemen, and EVEN FRONT has an even number of down linemen. You can eagle up and down and cover the center or leave him uncovered and still have either front. A good example of an odd front is a 50 front (5 DLM's) and an evn front (4 DLM's) is some kind of 40 front.

The odd front is synonymous with two-gap play at the line of scrimmage. From Nick Saban’s system at LSU to Rex Ryan’s system at the Baltimore Ravens (just to name the more prolific examples), the odd front continues to be utilized to defend many of the run game concepts presented at all levels of football.

As we point out in Defensive Installation Manual, odd fronts are defenses where there is a head up Nose Guard. Although they differ in that the 5-2 Defense is a 7 Man Front and the 5-3 Defense is an 8 Man Front, they are probably both most commonly seen with Cover 3 or some type of Man Coverage.