WGN meteorologist Tom Skilling has a blog.  He answered a question about the 76 All Star game which pitted the defending champion Pittsburgh Steelers vs.  a group of college all-stars.

original post here --

"Dear Tom,
I just heard a tape of the July 23, 1976, College All-Star Football game at
Soldier Field. The game was stopped by rain. What happened?
Tony Warren

Dear Tony,
The game started in very warm, muggy conditions with temperatures in the
upper 80s. There was a threat of severe weather, and it began to rain
heavily as the game began. Small hail and gusty winds accompanied the
thunderstorms. The rain ended, and the game continued on a sloppy field.
With the Pittsburgh Steelers leading the College All-Stars 24-0 late in the
third quarter the heavens opened up again as severe thunderstorms struck.
Winds gusted to 64 m.p.h. as the rain fell in torrents. The game was
stopped, but as the players left the field unruly fans ran out and knocked
down both goal posts. Even though the rain let up the game was cancelled. It
was the last College All-Star game ever played."

More details from wikipedia about the all-star game here

"The last game took place during a downpour at Soldier Field on July 23, 1976. Despite featuring stars such as Chuck Muncie, Mike Pruitt, Lee Roy Selmon and Jackie Slater, the rookies were hopelessly outmatched by the Pittsburgh Steelers, winners of Super Bowl X. Pittsburgh was leading 24-0 late in the third quarter when weather conditions made play impossible and the officials called for a delay. The players left the field and were replaced by unruly fans who tore down the goal posts. NFL Commissioner Pete Rozelle decided the game would not be restarted. Chicago Tribune Charities Inc., the sponsor of the game, elected not to bring it back for 1977."