This is bit of surprising news, but also indicative of lacrosse's higher profile and school's focusing on wins and losses more. Jacksonville's Director of Athletics Alex Ricker-Gilbert was pretty direct in the press release stating:
"We are very appreciative of Coach Van Arsdale's contributions to our program and the University, however, I believe the program needs to move in a different direction,'' Ricker-Gilbert said.
Additionally, Director Gilbert also stated that the school "will conduct a national search and assistant coach Alex Lopes has been named acting head coach." The school updated JU's coaches page which now only shows coaches Lopes, Carson Mann, and Adam Silva.
Coach Van Arsdale, the head coach for the last 5 seasons, was JU's second coach ever . Van Arsdale's coaching career reaches all the way back to 1988, when he took over the men’s team at Rochester Institute of Technology. Just prior to Jacksonville, Van Arsdale coached Division III's Colorado College for two seasons and In two seasons with the Tigers, posted a 25-3 record and won SCAC "Coach of the Year" honors both seasons. Before Colorado College, Van Arsdal was also an assistant at Penn State and Notre Dame.
Update I: I don't have too much now, but shout out again to @Horton1733 for the tip. All that is out there right now is this Tweet. I'll update with more as it becomes available.
BREAKING: Don Zimmerman has retired as @UMBC_MLacrosse coach.— Inside Lacrosse (@Inside_Lacrosse) May 2, 2016
Update II: @EdwardLeeSun's article on BOSS Zimmerman's retirement, which includes quotes from the coach himself, is up.