Combat is skill used for defending against attacking foes,Attacking foes and other uses involving the Robber Trade.
Uses in the Robber Trade-
Different levels of combat are needed to upgrade the trade from one to three. Ex: 10 combat is needed for level 1 robber trade, 20 combat is needed to get level 2 robber trade, so on...
How to train Combat-
To Train combat you need a Residence with the enhancement "Back Room". After you have the Enhancement you go to the Back room and Click on train combat in the left option screen.