Emyr Phillips really owes Scott Williams an apology after this, and if he already has, then he owes him another one. Floating one high in the air inside your own 22 with the opposition defensive line just metres away is never a good idea.
Once Tommy Bowe lined up Williams there really was nothing he could do other than knock on with the resulting scrum leading directly to Bowe crossing to pretty much guarantee at least a win for Ulster. (Update: Make that a bonus point win thanks to Rory Best crossing to make it 24-9)