Answer 1

The new version of Sturdy prevents being KO'd from full health. This means that if your Roggenrola is at full health it could get hit with any attack and not faint, being left with 1 HP at the most.

However, if Roggenrola has just 1 HP taken out of its health bar, it is completely open to being KO'd with one hit. This is likely what happened in your situation.

Answer 2

I would like to add to ~~Will~~...
Other way to be killed if you have sturdy is if they use a multiple hitting move
Examples:
-Double slap
-Double kick
-Rock Blast
etc.
I use double kick all the time on people with sturdy to one shot them and not take any damage
Good Luck!

Comments

Yes 1 of the pokemon (I cant remember what one.) But he used slap and killed him!!! Thank-you!!! Do you think it also might be  because his HP was down!?(It was down a tiny, tiny bit)
Once again Thank-you very very much

---

No, but it is possible.  Even if he has full health, he can still be KOd by multiple hitting moves.  I use Sawk to kill wild Boldoores on victory road in one turn before they attack.  But, sometimes I would forget and use a different move and they would NOT DIE!  Also if its HP is down sturdy doesnt work at all.;)