Counter arcing is method of gaining control of your barrel horses hips and shoulders.  Its keeps them soft and maneuverable if done correctly.  This barrel racing tips video from expert village give a nice explanation and demonstration of how to do this correctly.   If you have a horse that is shouldering a barrel or turning too soon, this is a great way to get control of their hip and shoulder so you can go into your turn upright and square, rather than having your horse pushing on you going into that turn.    Watch the video so you get a better visual of this barrel horse training tip.