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: Shares of outdoor equipment engine manufacturer Briggs & Stratton (NYSE: BGG) were taking a hit today, falling as much as 7% after rising 14% earlier in the day. The moves followed the company's fiscal first-quarter earnings report.

So what: The gains for Briggs & Stratton early in the day were easily explained by the company's earnings report. Though the quarter still showed a loss, the $0.10-per-share loss was much better than the $0.20 loss that analysts were expecting. Revenue also topped estimates, clocking in at $397 million versus the expected $346 million. As if that's not enough, management also set guidance for the full fiscal year above what analysts had been estimating.

But that all makes the stock's subsequent drop all the more head-scratching. While there's no clear driver of the pessimistic turn, trading volume for the stock is relatively low today, so it wouldn't take many decent-sized sell orders to drag down the market price.

Now what: There may be some temptation for investors to assume that "somebody knows something" and that's why the stock is declining despite the better-than-expected results. It's generally a good practice to resist that temptation. If you were invested in Briggs & Stratton because you like the business and were looking for an improvement in the fundamentals, this quarter should be welcome news for your thesis.

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