[kevkrom]

I can't say this is a definitive source, but according to this site "down by contact" requires (Rule 7, Section 4, Article I):

(e) when a runner is contacted by a defensive player and he touches the ground with any part of his body except his hands or feet, ball shall be declared dead immediately. The contact by the defense player must be the cause of the runner going down.

Note that last sentence: The contact by the defense player must be the cause of the runner going down. Hasslebeck was already going down before the incidental contact and was no longer in contact with the defnder when he hit the ground. Unless this is an outdated version of the rule, he was not down by contact when he hit the ground and subsequently fumbled. The original call of a fumble recovered by Pittsburgh should have stood.

[clawrence3]

Of course, that contact was not the cause - but didn't someone above point out the "bad" call ended up worse for Seattle?

[Echo Talon]

The contact by the defense player must be the cause of the runner going down.

If this were the rule, LOTS of games would have ended differently this year. I have never seen or heard of the game being called that way.