Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Best Buy (NYSE: BBY) reported Q3 earnings this morning, with headline numbers reading as follows: Same-store sales are down 5%, and profits are off by 4.4%.

So what: Neither of these numbers is what's worrying investors, though. What scared the pants off 'em were two others: Best Buy lost 110 basis points (that's "1.1%", to you and me) worth of its market share and saw its share price drop 15% in response.

Now what: According to management, rival retailers of flat-panel televisions and mobile computing devices stole customers during the Christmas sales season. Best Buy refused to enter into a price war with the competition, and fickle consumers opted to buy the same goods for lower prices, elsewhere.  So you can probably blame Wal-Mart and Target, hhgregg and Costco for Best Buy's woes this week.

A more productive use of your time, however, might be to buy these Best Buy-rivals, on the assumption that Best Buy's loss must logically be their gain.

Will Best Buy join the price war? Will it win? Add Best Buy to your watchlist and find out.

Fool contributor Rich Smith does not own shares of any company named above. The Motley Fool has a disclosure policy.

Best Buy, Costco Wholesale, and Wal-Mart Stores are Motley Fool Inside Value selections. Best Buy, Costco Wholesale, and hhgregg are Motley Fool Stock Advisor recommendations. Wal-Mart Stores is a Motley Fool Global Gains pick. Motley Fool Options has recommended buying calls on Best Buy. The Fool owns shares of Best Buy, Costco Wholesale, and Wal-Mart Stores.

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