Originally Posted by LizardState
That's as good an explanation as there is. The 5-technique is the textbook 4-3 DE.
That has become even more specialized with the emergence of the 5-tech DE designated pass rusher, sorta/kinda like the designated pass rusher OLB. Some of them are so good at being sack artists that offenses go to the no huddle just to disallow substituting for those guys
Well, the 5-technique is analogous to the traditional 4-3 base end (the LDE, the guy who lines up across from the RT who was traditionally a big ugly). Bruce Smith was a 5-tech, Reggie White could have played that position (he was an LDE instead).
In the modern NFL everything is topsy-turvy though. TEs comparatively rarely block on passing downs, so 4-3 defenses want a base end who can rush the passer, and so offenses need an RT who can pass block effectively... and so the difference between the blind-side and the other-side is sort of decreasingly relevant. I mean, heck the eventual superbowl champions moved their best pass rusher away from the blind side in the offseason.
But if you think about the stereotypical classical (say mid-90s) 4-3 defense then there's a lot in common between the base end and what you look for in a 5-tech, specifically in terms of being able to stand up against double-teams as well as provide some pressure (though not necessarily sacks). In the classic 4-3 defense, the designated "pass rusher" in the RDE would oftentimes line up in a 7, 8, or even 9 technique. I believe Jimmy Johnson's defense during the Cowboys dynasty had his two defensive ends in 7 and 9 techniques and made up for it with two DTs stouter than we would think of as an "under tackle" these days.
But the moral of the story these days is if you see a defensive end who is big and powerful, or a defensive tackle who is long and athletic, then you might think that guy can play the 5-technique position. Traditionally 5-techs are 6'3"+ 300+ but the height is largely for sufficient arm length (so you can more easily disengage from blockers) and the weight is largely for sufficient power to stand up against double-teams. If you had like a monstrously strong 6'1" guy with freakish 35" gorilla arms who only weighed 270 lbs, that guy could play 5-tech too. "How they play is more important than how they weigh" as it were.