A "shirt fight" is a very brief type of fight that occurs when two parties begin to get aggressive with eachother, yelling first and then usually one or both people grab hold of the others shirt and yanks at it or uses it to shake that person they are yelling at. A "shirt fight" differs from a "fist fight" in that no physical blows are thrown, but cannot simply be defined as an argument because it usually results in a ripped/stretched shirt.
Person 1: "I heard Joe and Bob got into a fight last night at the bar; are they still mad at eachother?"
Person 2: "Naw, it was just a shirt fight they were cool later that night."
Person 1: "A shirt fight?"
Person 2: " Yea, you know they got into it yelling and touseling with eachother and Joe's shirt got a little ripped."