There are many different fronts in all levels of football. In each defensive front, coaches and players need a way to communicate different alignments when setting up against an offense. To do that, we use a numbering system that tells us where each defensive player is aligned in comparison to an offensive lineman. If a defensive lineman is directly in front of an offensive lineman, they are an even number. If the defensive player isn’t directly over the offensive player, they are an odd number. There are some nuances, based on whether the the player has an inside shade or not. If they do, an “i” denotes that.
A player aligned directly in front of an offensive tackle is a 4-technique. A 4i would be on the inside shoulder of the tackle.
4-techniques are usually 3-4 defensive ends. They’re a little slimmer than 3-techs and often work against tackles by alignment. They have to be impact players in both the run and pass game. However, 3-4 ends aren’t usually premier pass rushers. 4i players are becoming more and more popular and are a staple in fronts used by Brandon Staley. The 4i alignment makes it difficult for offenses to leave them as solo blocks.
True 4-techniques aren’t all that common in the NFL. They often lean more towards being defensive tackles that are split out wider to help hold the point of atttack and allow the linebackers to run free.