Possibility

[Younghawk]

When  {Possibility Storm} is on the field does it effect blood rush effects?

[Keyeto]

No. Bloodrush is an activated ability; it does not count as casting a spell.

[Paraluke]

Bloodrush is in synergy with  {Ruric Thar, the Unbowed} as you are discarding and not casting.

[TheRagingMage]

Does exiling the spell with that card keep it from being cast?  I would assume so.

[Keyeto]

Does exiling the spell with that card keep it from being cast?  I would assume so.

The spell will still be count as cast, but it will be exiled before it can resolve. "Whenever a player casts a spell" type effects will still work, since you do cast the spell (otherwise, Possibility Storm wouldn't go off in the first place).