The Standard & Poor’s 500 Index fell the most in eight months to erase its gain for 2015, and European shares capped their worst day this year on concern Greece will exit the euro. Greece shut lenders and imposed capital controls, a measure that will deepen the country’s recession and risk driving it toward an exit from the euro. European leaders raised pressure on the country to re-engage, saying it’s up to the government to step back from the brink and stay in the euro. “This is going to get quite messy between now and the weekend,” Kevin Caron, a market strategist and portfolio manager who helps oversee $170 billion at Stifel Nicolaus & Co.