Wow, LOTS going on here!
One thing that hasn't specifically been mentioned above is the impact of a circle in a large fleet. If you're racing in an 8-boat fleet, a circle probably won't hurt much unless the offendor is in front of most of the fleet, and they're tightly packed. If the offendor blows it in front of a 30-boat or larger fleet, particularly at the first weather mark, he could easily lose a dozen boats in a highly competitive fleet. This may factor in to whether you decide to protest.
Having raced long enough, been to enough seminars, served on enough mark boats, as PRO, and on PCs (where these exact protests have come up time and again), here's what I've come away with over the years...
Generally speaking in terms of etiquette, it's been well said above. All things being equal, it's always better to spend your time in the bar than the room, especially over touching a mark.
As Rick mentioned, distance and angle are HUGE factors. We are trained by the IROs and IJs to ignore these things 99.999% of the time if witnessed by a mark boat. Unless you have the most amazing angle ever, AND there are no sailors around to protest, it didn't happen. Period.
If those two high standards are met to the PRO's satisfaction, the next step is for the PRO to approach the sailor, explain the situation and ask him to retire. Again, it would never get this far with a good PRO, unless the PRO knows he has to do it (no competitors were witnesses) AND has a rock-solid case, a combination which is actually pretty rare.
The reason I mention the RC point of view first is simple. For most sane people, the same logic should be applied as a fellow competitor. First, were you at the appropriate angle and distance to KNOW the mark was touched? If so, you're close enough to hail protest, and must do so per the RRS, as mentioned by others above.
If the guy doesn't spin, then you have the option to follow up with the protest, or let it go, also as mentioned by others above.
Personally, unless I see the mark get "dimpled" and spun, I wouldn't feel comfortable protesting, whether as a sailor or RC. When on PC, I wait to hear these things specifically described before ruling as DSQ.
Hope this helps.
Mike
