Lassic attended North Rockland High School, where he helped his team achieve three straight Section 1 Class A bowl wins.
He was named the New York State large-school Player of the Year, All-state and a USA Today's High School All-American.
As a junior, he was the backup running back behind Siran Stacy, posting 70 carries for 368 rushing yards (third on the team) and 2 touchdowns.
[3] The team was forced to start him in the first two games (both losses) after Emmitt Smith’s contract holdout extended into the regular season.
Although Smith signed in time for the third game against the Phoenix Cardinals, Lassic still started and led the team in rushing with 60 yards on 14 carries, while scoring his first 2 touchdowns during a 17–10 win.
In the eleventh game against the Miami Dolphins, he was demoted to third-string running back after being passed on the depth chart by fellow rookie Lincoln Coleman.
We have a flow and he isn't able to see it", Nate Newton said, "Lassic was a nice kid, but if we expected to get back to the Super Bowl, we needed Emmitt in the lineup".
[6] In Cowboys lore, he is remembered for being the starting running back for the first two games of the 1993 season when Smith held out in a contract dispute.