well it was specifically when rags does a dead spike at a significant distance, and tries to follow up with 5b. it's the same thing as 5a, but instead throw. look at the hitboxes, seems like it could work..
essentially 6 frame startup
http://www.dustloop.com/guides/bbcse/hitbox/tsubaki/groundThrow.html
8 frame startup, 13 frame for long range
http://www.dustloop.com/guides/bbcse/hitbox/ragna/5B.html
Dead spike-> + 3 (more if meaty)
so yea, obviously it loses if they're close enough.
anyway, I did specifically mention theory because it is theory, and I have no interest in 'theory fighting'... have to test to see if it's actually practical..