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Both answers above are correct and great ones. From a strategical point of view, formally blocking russian IPs does not have any SEO effect in your case, because - as a business - you don't even need an SEO strategy for the Russian market.

Many SEO shops don't have overhead.  Most work in shared co-working offices, or coffee-shops etc.  Just because they appear like a big-time agency, most are just mini-teams looking to make an honest living. That being said, if I want a comprehensive list of respected people in the SEO industry, I'd confidently start with this list http://www.seomoz.org/article/search-ranking-factors#contributors. Best, Corey

I have seen changes like this where it appears that a competitor has been spurred by being pushed out of the number 1 or 2 spot to take a look at their optimization for that particular term. Something else that could possibly affect just one keyword is the mix of anchor text in your link profile. There is some great discussion of this in the latest Whiteboard Friday - [Beyond Exact Match Anchor Text to Next Generation Link Signals.](Beyond Exact Match Anchor Text To Next Generation Link Signals - Whiteboard Friday "Beyond Exact Match Anchor Text") It might be worth taking a look at your link profile to see if there is any obvious difference in the mix of terms for the keyword that has changed. Hope that helps, Sha