The over and under front really describe the shift of your defensive linemen. Without getting into a long explanation, the under front shifts your defensive linemen to the weak-side of the formation.
The over front shifts your defensive linemen to the strong side of the line.
Note: in madden this called 4-3 normal but it is still technically an over front
If you look at the diagrams and focus specifically on the defensive linemen. You can see in the first picture the linemen are shifted to the left (weak-side away from the TE), and the in the bottom pic the linemen are shifted to the right(strong-side toward the TE).
The reason for this is you may want to put your strongest players to one side or the other depending on where the offense may run. You can see the 3 (technique) moves in both pictures. This is because between your two defensive tackles he is usually the best. Think Warren Sapp or Suh from the Dolphins type of player. If the offense in running to the weak side of their formation you may want to get in an under defense to put your best DT and your strongest run defenders(your defensive line) to the weak-side of the formation. Now the offensive is running into your strongest run defenders. The same thing but opposite for the madden version of over. The madden version of over is basically the under flipped. So if they are running the strong side then you may want to get in the over front.
The over and under front really describe the shift of your defensive linemen. Without getting into a long explanation, the under front shifts your defensive linemen to the weak-side of the formation.
The over front shifts your defensive linemen to the strong side of the line.
Note: in madden this called 4-3 normal but it is still technically an over front
If you look at the diagrams and focus specifically on the defensive linemen. You can see in the first picture the linemen are shifted to the left (weak-side away from the TE), and the in the bottom pic the linemen are shifted to the right(strong-side toward the TE).
The reason for this is you may want to put your strongest players to one side or the other depending on where the offense may run. You can see the 3 (technique) moves in both pictures. This is because between your two defensive tackles he is usually the best. Think Warren Sapp or Suh from the Dolphins type of player. If the offense in running to the weak side of their formation you may want to get in an under defense to put your best DT and your strongest run defenders(your defensive line) to the weak-side of the formation. Now the offensive is running into your strongest run defenders. The same thing but opposite for the madden version of over. The madden version of over is basically the under flipped. So if they are running the strong side then you may want to get in the over front.