A biotech executive committed insider trading when he bet on a competitor’s stock, believing the shares would rise when news about his own company hit the market, a jury found Friday. The civil-fraud verdict against Matthew Panuwat, former head of business development for pharmaceutical company Medivation, marks a significant expansion of insider-trading law. The law has mostly been used to punish people who misuse nonpublic information by buying or selling their company’s stock before a big share-price move—or tipping others to do so.