A boat has right of way when another boat is required to keep clear of her. [[ISAF RRS] Section A defines the various right-of-way rules however, some rules in Sections B, C and D limit the actions of a right-of-way boat.
If you are not the right-of-way boat then you are may be referred to as either the give-way boat or the keep-clear boat.
Can a boat that has received a penalty have right-of-way?[]
Yes it can. However, once the penalized boat has started taking a penalty turn it is required by rule 21.2 to keep clear of any boat that is not taking a penalty turn.
When is a right-of-way boat considered to be a "pen hunter"?[]
A penalty hunter is a right-of-way boat that has deviated from her proper course with the intention of causing another boat to receive a penalty. In match races (i.e. races involving just two boats ... such as the Americas Cup challenge) pen hunting is an accepted tactic. In a fleet race, however, the aggressive maneuvers of a pen hunter are often frowned upon.
Since it is very difficult to determine intent this is a purely subjective matter. Indeed, there is no ISAF rule that prohibits pen hunting however there may very well be a sailing instruction or house rule that does prohibit penalty hunting. If you are accused of pen hunting in a fleet race then you may quickly find yourself in a kangaroo court and shortly thereafter you may be staring at the message: what message do you see when you are kicked or banned?
If you know the racing rules of sailing and you routinely assert those rules aggressively then you'd better be prepared with a good defense in the event that you are wrongly accused of pen hunting. Sadly, it is the practice of many hosts to shoot first and ask questions later.