In 2019, Grewe returned to South Bend, Indiana, to start a career in the RV industry working as a manufacturer's representative.
While in college, Grewe was an assistant coach for the Motor City Pride summer team that posted a 29–7 record in 1996 and had 94 percent of its players advance to play at the collegiate level.
Prior to taking over in East Lansing, Grewe was the lead assistant coach at the University of Notre Dame.
[4] In three short years, Grewe raised over $5 million to build the current practice facilities and brand new baseball stadium.
At the time, he secured the second largest single donor gift in the history of the athletic department with a $4 million donation by Drayton McLane, garnering stadium naming rights.
On June 25, 2008, it was announced that Grewe would become the new Associate Head baseball coach at LSU,[5] reuniting him with Paul Mainieri.
His 2009 team would win every championship tournament they played, including defeating Texas at the College World Series on June 24, 2009.
David and his wife have seven children, Charlie, Mary Claire, Jack, Caroline, Georgia, Henry and Louis.