William J. "B. J." Prager is a retired professional lacrosse attackman who played professional field lacrosse in the Major League Lacrosse (MLL). He starred as a member of the Princeton Tigers men's lacrosse team from 1999 through 2002, where he was Ivy League rookie of the year, a three-time United States Intercollegiate Lacrosse Association (USILA) All-American (twice third-team, once honorable mention), a four-time All-Ivy League selection (three-time first team), a team captain and an NCAA Tournament Most Outstanding Player of a national champion team. For over a decade, he held the freshman goal scoring record at Princeton.