[ScottM]

It might be better to refer to defense as "active" and "passive".

Active defense would involve your robot agressively trying to stop your opponent's offensive moves through some sort of robot to robot interaction that you initiate. The GDC has effectively eliminated most avenues of this type of defense in the rules. (Defense on the trackballs being one exception)

Passive defense would involve trying to stop your opponents by being in their way, without actively initiating robot to robot contact. The rules allow you to be standing still anywhere on the field, as long as you aren't moving and there is a clear lane around you.

One strategy of using a passive defense would be to position your robot in front of your alliance's trackball on the opposing alliance's overpass, which could hinder attempts by your opponents to dislodge it. This is perfectly legal within the current rules, as long as you are not moving to impede the opposing robots.

Personally, due to the nature of this year's game, I would not discount the possibility of a successful passive defensive strategy.