One day while at the bar Marshall makes a prediction that the Boston Celtics will lose. He bases this on a correlation his computer has spotted between Celtics losses and activity in the Van Allen radiation belts. Sam uses Marshall's information to make himself some money.
Carla, who flirts with Marshall dated him soon afterword, then told him he was the father of her child - which she knew was a lie. After being confronted and prodded by Diane, Carla admitted to Marshall that he wasn't the child's father. Although Sam tried to convince Marshall to stay with Carla, he declined and left. Lipton is never seen nor heard from again.
Marshall is painfully shy and nerdy, but well liked by the Cheers employees. He is also very intelligent. He got into cybernetics, as he puts it, because he enjoys "integrating formally unassociated supporting elements to maximize a probability ratio by functionally interweaving the input data."