Board Thread:Speculation House/@comment-6500074-20130310094020/@comment-3146930-20140329210935

72.71.242.19 wrote: Perhaps Weiss got her scar from her father during her childhood when the Faunus were killing off people close to her family. They did say that he "came home furious" and that she had a "very difficult childhood".

One popular theory is that the Armor in her trailer is a metaphor for her father, who would abuse her (resulting in her scar). She then fought back against him and left to become a Hunter. This is all just speculation however.