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1.
When someone in a recreational sport guards only one person through the entire game, usually because of a crush or something of the sort.
"Bro, in gym today Sally would not stop covering you. Thats a guard on if I've ever seen one."

"Hey, Mike... I'm kind of worried about you. At the Y earlier today, you definitely had a guard on for Jim. Does your wife know about this?"
by Legsman February 10, 2010