Defense part of Sflex slot

So a longtime $ league of mine has added Def as an option for the SFlex slot. Since it’s not an option in any draft prep/cheat-sheet I’ve ever seen, anybody have any advice?

I suppose in a really tight pinch, say your best SFLEX options are all either hurt or on bye weeks, or perhaps handcuffs that just aren’t projected to play this week, but you do have an extra defense on your bench with a favorable matchup this week? You could play them there. That said, I wouldn’t plan to do it. This is worst case scenario stuff, unless your league really has favorable scoring for defenses?

Let’s just call this an “interesting” league setting. I honestly can’t see a scenario where you want to start a DST over a QB. This seems more like a way to play for upside during a difficult week versus a setting anyone would need to plan around or strategize for.