Straight ankle lock. what is it?

So the straight ankle i was taught, is supposed to cut into the lower part of the calve. But today i kept getting tapped by an actual straight "ankle" ankle lock. it felt like a toe hold but in the SAL position. I kept trying to use defend by straightening my leg. didnt work. Has anyone else heard of this?

I'm not sure if this is what you mean, but a straight ankle lock done low on the ankle the way Reilly Bodycomb teaches it in the SL4NG DVD set works and feels exactly like a toe hold. Reilly even describes it as a toe hold done with your armpit.

It is how I do the straight most of the time.

I think you are referring to the foot flex. Its about the 20:10 mark.

https://www.youtube.com/watch?v=9Ap-8os2e4g

If so the standard boot defense and sit up escape is the same as a standard straight ankle lock. You need to make sure when you put the boot on you push your leg through so his grip is higher up your calf.

A "straight ankle lock" could mean an "Achilles lock" which you seem to be talking about being taught (its most commonly taught in most BJJ gyms) which grinds on the Achilles tendon. Or it could mean the "foot flex" that Zog mentioned where you stretch the ligaments on top of the foot. OR it not TRULY be a STRAIGHT ankle (don't tell the IBJJF but these can be a twisting sub like a toe hold ;) )... just look like one and be executed in a similar fashion. This last one seems to be what you are describing because what it does is attack the ankle in a toe hold type of way but using a "straight ankle" grip. In events like NAGA with an open rule set, I ALWAYS use this style because I feel it is more adrenalin proof. It is changed into this type of sub by bringing your shoulder and elbow back and lining your back arch up with the side of their ankle. This is the trickiest one of these 3 to execute and the least common, its usually done by more experienced leg lockers...

Like Zog said though, technically the boot is still the "defense" but many experienced ankle-lockers have gotten good at beating that defense.

Hope this answered your question :)

I cover all 3 in the video, it all starts around the 17min mark.