Jack Soapy Shapiro was 5 feet 1/2 inches tall and weighed 119 pounds
That statistic is not kept by the NFL.
There is no required weight in the NFL. The smallest player I can find record of for this season is 178 pounds.
The smallest running back in NFL history was Butch Meeker. He played two games in the NFL and score two touchdowns. He was five foot three inches tall.
"Mini" Mack Heron Boston Patriots
Ray Rice, HB for the Baltimore Ravens, at 5'8"
For the 2013 season, Denver Bronco WR Trindon Holliday is the smallest player in the NFL. He is 5'5" and weighs 166 pounds.