That's not true
In 1962 against the Baltimore Colts, he rushed 14 times for 11 yards. An average of 0.79 yards per carry. It would be pretty much impossible for him to play that game without a negative carry. Two other times in the regular season he averaged below two yards per carry with at least ten rushes, rushing for 20 yards on 13 rushes (1.54 YPC) and 24 yards on 17 rushes (1.41 YPC). Also, in the playoffs against the Giants, he seven times for eight yards, averaging 1.14 yards per carry (fun fact, the Browns lost 10-0, and Pat Summerall kicked the XP and field goal) .
Another interesting fact is that he frequently recorded receptions for negative yardage, finishing games with negative receiving yards six times in his career, where you saw game stat lines like two receptions for -12 yards, or four receptions for -7 yards (no idea how that happens on four receptions).
