Nebraska assistant coaches Tolly Thompson and Steve Hamilton have resigned from their positions on the Nebraska coaching staff effective immediately.    Reasons for their departure are unknown, though sources close to the program have revealed that a confrontation took place between Hamilton, Thompson and head assistant coach Shawn Charles.    Hamilton served as the co-head assistant coach alongside Shawn Charles. He completed his second season with Nebraska this past season. Before coming to Nebraska, he spent three seasons as an assistant coach at Northern Iowa under current Nebraska head coach Mark Manning.    Thompson served two years as Nebraska's strength and conditioning coach. He also served at Northern Iowa under Manning as a volunteer assistant coach in 1999-2000.    "I am sad to see them leave, but I wish them good luck," stated Manning, who will enter his third season as the head coach at Nebraska this year. "Tolly and Steve have chosen to explore other opportunities in their careers. They helped our program while they were here and will be productive in whatever else they do as well."    As a collegiate competitor, Hamilton was known as one of the top wrestlers in Iowa State history. He was one of six Cyclone wrestlers to earn All-America honors four times, competing from 1988 to 1992. Hamilton was voted ISU's Most Valuable Wrestler as a junior and senior.    Nebraska's all-time winningest wrestler, Thompson compiled a career record of 157-21 from 1993 to 1997. His 157 wins place him ninth on the NCAA's all-time wins list. He also tops the Nebraska's career fall charts with 72 (53 pins, 19 technical falls).  He was a three-time NCAA All-American and won the 1995 NCAA championship at heavyweight.    Hamilton and Thompson could not be reached for comment.. A search for new assistant coaches will begin immediately.