He was a member of the school's basketball team, the Vikings, which won or tied for the Chicago Catholic League championship for four consecutive years from 1975 to 1978.
[2] Stack, however, was unable to play in the Vikings' semi-final and third-place games, which were both losses, in that year's tournament due to an ankle injury he suffered during the team's quarterfinal victory.
[3][4] In the 1977–1978 season, the Vikings won their first 27 games before losing 42–41 in the sectional round of the 1978 IHSA Class AA tournament to the also 27-0 and eventual state champions Lockport Township High School.
[27] In September 2004, Stack was convicted of misdemeanor battery for his involvement in altercation with another man at a youth baseball game in Schaumburg, Illinois on July 4, 2004.
Stack was sentenced to one-year court supervision and ordered to visit terminally ill children at a local hospital in December 2004 when the Timberwolves were scheduled to play the Bulls in Chicago.