WoWInterface - Target Castbar

Depend if it is in the HUD or in the unit frames... more or less the same concept either way.

For the HUD, edit [ Interface > AddOns > nUI > Layouts > Default > HUDLayouts > {HUD mode} > nUI_HUDSkins_{HUD mode}_Target.lua ] and search for the section that looks like this...

Code:

["Casting]" =

{

    -- blah blah blah

},

Either delete or comment out that section and the casting bar is gone. For the unit frames, same thing, just different files. It should be pretty obvious though if you look at the directory structure in [ nUI > Layouts > Default ]

BTW: If you raid any, or do PvP, I would argue getting rid of that bar is a bad plan.