Ball thrown off pitch

[PaulDG]

Ulster vs Scarlets on Saturday.

Defender (Ulster, I think) threw the ball off the pitch - I thought accidentally. Next thing I see (as usual, Sky talking over the ref and showing clips of some event 15 minutes ago), there's a scrum.

Anyone know what the decision actually was? Was a penalty given and scrum option taken?

Or is a scrum the proper decision for an accidental throw? (I'd have thought it should be a line out - am I doing it wrong?)

[Glyndwr]

Haven't seen the incident, but believe the following should cover it:

Deliberately thrown off the pitch - penalty
Ball goes off because of misplaced pass backwards- line-out
Ball goes off because of misplaced pass forwards - scrum