At what temperature do you think it is pertinent or advisable to cancel an outdoor sporting event?

Lately around here the temps have been hovering around 98 to 107 deg. (yey!!), many people are cowering hunkering down in their homes under the A/C. Some people were still out doing athletics, but many who have dogs are keeping them inside. That made me thinks if you would not let your pet out in the heat, would one go into the heat themselves to play sports or allow their children to do such? At what temperature should a sporting even be cancelled? Would it determine how much physical exertion is needed, like running or jumping? Would it depend on how much is worn, such as beach volleyball with minimum clothes, as oppose to football with full pads and helmet?