NEW YORK—The head of the New York Stock Exchange on Thursday called for regulators to change rules that make it difficult for the NYSE to compete for stock orders, as the market share of exchanges has dwindled versus off-exchange trading platforms during the retail trading boom. “On exchange, we are artificially constrained from competing for pretty much half of the market,” said Stacey Cunningham, president of Intercontinental Exchange Inc.’s NYSE. “It’s like we’re in a bullfight, and sure, you can beat the price on an exchange if you’ve drugged the bull and starved him for two weeks,” she said at an annual conference held by the Securities Traders Association. U.S. Securities and Exchange Commission Chair Gary Gensler has said his agency is revisiting regulations he says may create an unequal playing field for exchanges versus broker dealer-run trading platforms. One rule the SEC is reviewing is referred to as the …