Brennan, who also coaches on the club level with Team Maryland, played collegiately at Division III DeSales University. As a senior, he was named a United States Intercollegiate Lacrosse Association Scholar All-American and was a two-time All-Freedom Conference selection. He set five school records for the Bulldogs: ground balls in a game (21) and season (159); faceoff percentage in a season (.700) and career (.664); and season faceoffs won (275). During his junior season, he ranked in the top five in Division III in faceoffs as DeSales finished the season ranked atop the national leaderboard in percentage.

A local product, he played for St John's Prospect Hall in Frederick and was named to The Frederick News-Post All-County Team.

Gmeiner resides in Frederick working full-time as a licensed financial planner for Turning Point Benefit Group.