From Webkinz Insider Wiki
In the running competition your pet will run against 4 other pets. There are 4 groups called a "Heat" and each heat has 5 pets total in them. They will only show you 3 of the 4 heats. The winner of each heat then will go on to compete against each other. The winner of that last run will be the winner of the competition. This is the only competition (in quick events) of all of the events where entrants can see most of the pets who have entered compete, because of the different heat categories.
On Webkinz Newz new events have been hinted at, in addition to the original two. They said:
"We have two more events ready to go for the Stadium. We have both of these events on the plan for 2010. The first of these will be a Running event, so keep working on your pet’s speed at the Kinzville Academy."
During the Twitter contest in April 2010, the Creative Director mentioned that one of the events would be racing.
The running competition is in the Webkinz Stadium at this point and can be played.
Ready Room Furniture:
-Royal Blue Flooring
-Ultra Modern TV
-Speed Class Treadmill
-Water Cooler Fridge