Capping was a word used back in the late 80's early 90's that described a form of word battle. Saying someone's shoes were bought at K-Mart would be a form of capping. Basically it's a form of putting someones cloths or style down. It was common to hear someone say "ohhh you got capped on!"
"You must go to church allot with all them holes in your shoes!". The holes in the shoes meaning they looked holy. Someone else who heard the cap would say something like, "You just got capped on!". Capping was common with wannabe rappers