sentences:  Duffield began his career as an 18-year-old with Sheffield United in 1987.In his time at Bramall Lane he made 58 league appearances and scored 16 goals, including a perfect penalty record of 7 scored from 7 taken which is a club record.Duffield also holds the club record for being the first Sheffield United substitute to be substituted after playing 14 minutes at Craven Cottage against Fulham on 29 April 1989.