Allstate ( ALL) is one of the giants in the property and casualty insurance space. The company, which has a market capitalization of $16 billion, has its tentacles deep in the U.S. economy, with insurance products protecting against a variety of risks. Since the beginning of May, shares of Allstate have plunged. After peaking at $34.40 per share on May 3, shares have dropped to their current price of around $30.67 per share, a loss of more than 10%. The stock market was certainly weak in May, but the S&P 500 was only down 1.4% for the month. I would have expected Allstate to outperform the index because it's a defensive stock with consistent cash flow irrespective of economic activity. The market, however was apparently selling Allstate instead in anticipation of higher claims due to increased tornado activity. From a valuation standpoint, the selling wiped out what had been a stellar first-quarter performance. Allstate beat estimates by 25 cents per share in the period ended March 31, which had lifted shares by more than 10%. Easy come, easy go, I guess. Going forward, I would not be swayed by the headline carnage of the current tornado season. Use the selling in Allstate as a buying opportunity. Big bets on Allstate come from Arnie Schneider's Schneider Capital Management, at 1.6% of the total portfolio, and Richard Snow's Snow Capital, with a 2.3 million-share position.