I guess it's different in different parts of the country. I've ridden NETRA, VCHSS, FTR and Mid South harescrambles. In most cases they cover this at the riders meeting. "If someone comes up behind you it's because they are going faster than you. Get out of the way." Sure there are exceptions. Sometimes there are long sections of single track woods trails where you just can't get by. I was in front of Scott Summers (being lapped of course) in a section like that. He yelled, I moved. Can you imagine me being so arrogant as to hold him up just because I was racing too?