On a warm Saturday in April, most of the baseball diamonds and soccer fields in Red Hook were deserted. Vast tracts of brown grass sat empty behind locked gates, four-foot-high weeds blowing in the wind. Just a few years ago, if you came down here on a Saturday, there were hundreds, sometimes thousands, of adults and children — some playing soccer, baseball or softball, others taking part in the shot put and long jump, crowds of parents and friends cheering them on.

Wally Bazemore, who grew up in the nearby Red Hook Houses back in the 1950s, played on these fields as a kid, and later coached Little League. His son played here as well. “Everyday we played out here,” he said, staring out at the empty land. “We had a great time.”

But since 2015, most of the Red Hook fields have been closed because of lead contamination in the soil. A $107 million cleanup by the New York City parks department has been delayed, leaving residents, coaches and parents anxious and confused.

“We need our fields back,” Mr. Bazemore said. “But safe.”

Problems started in 2012 when the parks department and the city’s health department learned of a dissertation by an environmental scientist who identified close to 500 lead-smelting sites around the country. One of the smelters once stood in Red Hook, right across the street from the housing projects and right on top of some of the playing fields.