Impetigo is a very contagious form of Staph. It usually presents in "pimple-like" clusters and is very fond of the hands and face. Hands being the elbows to fingers.
Here's some more information.
http://www.mayoclinic.com/health/impetigo/DS00464.
Usually it's not the gym or schools fault. It's the dirty person you may have rolled with. Easy ways to prevent rashes is to keep your skin intact. Which means moisturizing right after you get out of the shower. Showering strips the skin of it's natural and essential oils. Dry skin is weak skin. Keep any broken skin covered. Do not shave right before or after rolling. Do not scratch, EVER! Finger nails are breeding grounds for bacteria. Any time a rash is present it got there because your skin was not intact or healthy.