This is pretty similar to the Lifestyle change thread. It's wise to have your clothing choices match your activities. Heels and grass (or any soft turf) don't mix. I've yet to see a woman walk gracefully in heels over a lawn, and I hate to think of all the beautiful shoes that have been ruined by this.
I wear heels to work and out shopping or out for the evening with hubby. To my kid's sporting eveents, I steer clear of any heel that could possibly dig into the earth. (Or any heel that would be uncomfortable to stand in for an hour or more.) You can wear a chunkier heel, especially in a boot. You could wear sporty track shoes. You could wear low mules or even oxfords. The key is think ahead. Will you be standing? Wll the ground be wet? Will you be able to jump up and cheer--gracefully? Will you have to walk across any soft earth?
Today, I planned my entire outfit around the messy weather and the need to wear appropriate footwear.