Suppose I am operating a busy HF contest, and I have found an open frequency to call CQ. I make a number of contacts, and then suddenly another station starts to call CQ right on top of me. The other station is either matching my frequency or within about 1.5 kHz, so filtering is not a practical option. His signal strength is greater than most of the stations that are trying to contact me, so any time he transmits, I lose any exchange details. There isn't really any room for me to adjust my frequency (it's a busy contest). How should I manage this situation?
The first thing to realize is that you can't make anyone move. So you can contact him and tell him (politely) the frequency was in use and he's interfering with you. At that point he may apologize and QSY. Yes, that does work, I have seen it happen. Or he'll tell you to pound sand or just plain ignore you.
If that happens, there is really nothing to be done but to try and find a new run frequency. If it's real busy, then spend an hour on S&P and try to pick up some multipliers while keeping an eye out for a new run spot.
The last thing you should do is waste time on it. A good score is all about rate. IF you are struggling and he won't move, move or go S&P for a while. Or depending on the rules and schedule, take a break now.