A bump is made when any form of contact is made with the boat in front; however, outright collisions are neither necessary nor encouraged. Alternatively, if possible, an overtaking-bump occurs when the stern of the chasing boat completely passes the bow of the boat in front. This is relatively rare simply because it is easier to make contact with a rival boat than it is to overtake it. A bump of this kind usually only occurs when a boat crashes. Under the current Cambridge rules, to overtake merely requires the pursuing boat to draw alongside the other boat's bow ball; side by side is good enough, and in the early part of the course a bump is deemed to occur when the bowball of the chasing crew passes the cox of the crew being chased.