Hard to tell, tho right now I would have to agree with Kevin.
None of those scars look at anything much more than just kicks or your boy getting into trouble with general horse playing BUT having said that, it almost looks like there might be a patter to the marks on this legs. Keep in mind that like people, some horses will scar more easily than others. I would stay clear of pink skin, but would throw some ointments on there if you want to try to regrow some hair in most of those patches.
To be honest, if I were to walk passed your guys at a show, I would never notice those marks. He's got a really nice coat as it is.