You know what in the UK they don't even allow the adults to compete in the sports day anymore because the schools fear an injury like this. They are insured against any claim on the children but not if an adult gets hurt so they don't allow us to race anymore!
I remember turning up to my eldest son's first sports day and thinking that us parents will get a chance to join in the fun. I'm sure my son would have been happy to see me make a fool of myself just like you did :-)
Nice to know adults are not allowed to compete in intersports but here, Schools see it as fun and the mistake they sometimes make is not grouping the parents or adults. It gets clumsy, leading to falls and embarrassment. All the same, its an experience.