Things are kinda crummy right now for the rapier community for a bunch of reasons.
So I did some point control tonight and now we're gonna look at Plate 25! (It's on the right. It's also really cool.)
Prime! That weird guard that everyone says "what good is that really?" about. This! It is good for this! (And other things too, but this!)
Anyway. "This wound of first against a third would happen this way."
Fencers begin at misura larga, in Third, on the outside. Each is forcefully pushing their blade against the other. (This is one of those positions that none of us should ever want to be in, but here we are.)
You should quickly turn their hand into First. While you are doing that and lifting your hand, you advance toward the opponent and hit them. (Straightforward, which is why I didn't really break this down into steps like I have previously.) I've found that it works well if you're rotating around with the wrist, and not a bigger arm motion. The strike can feel odd because it's not necessarily in line with the blade like a lunge, but it does work out.
Fabris points out that your opponent's sword should be underneath yours; you're basically yielding around it to keep your point free and kill them. He also points out that, again, being in the original position is bad, and you don't want to be there.
That's it! Really short, but super cool.