Spectators crowded around a temporary wooden rink at the Sigma Nu fraternity house on Saturday for the annual Winterfest broomball tournament. The event, organized by the Sigma Nu Fraternity in cooperation with the U-M Interfraternity Council and the U-M chapter of the Panhellenic Association, has raised more than $225,000 so far for Autism Alliance of Michigan, Fisher House Foundation and the Women’s Center of Southeastern Michigan. Donations f…