Before track events it is pretty common for people to wear warm up gear to keep their muscles from getting tight. I always wear tear away pants because of an incident that happened to me in high school.
I was supposed to run the mile on a cold November morning. I had been wearing a pair of loose fitting sweat pants. When it was time for me to get ready I went to take the sweat pants off but didn't take my shoes off. I was hopping around on one foot trying to get them off when I stumbled, fell, and twisted my knee really badly. I couldn't run the race that day and had to stay out of track for a few weeks.
I can't blame it all on the pants but that was a part of it. Now I wear tear aways so that I can keep both feet firmly on the ground.