All this talk about turf wars has me itching to jump in! Yes, there are lots of unwritten rules about how close you should get to another angler's water if he has a chance to win, but those "rules" are far from enforceable, and as the season goes along there are lots of other factors that come into play.
For example, although an angler might not have a realistic chance to win the tournament, a good finish could put him in the Bassmaster Classic or earn him valuable AOY points or just give him a check that will allow him to keep fishing professionally.
Those factors don't get much press, but they're huge, and they get bigger as the season progresses. When you see two anglers bumping boats out there and only one is in position to win the tournament, you sometimes have to look a little deeper to figure out why the other angler is there. Is he fighting for a Classic berth? Does he really, really need a check? Maybe it's just bad blood between the two.
If you put late season tournaments on bodies of water that fish "small" (and Lake Michigan is fishing small this week), these sorts of turf wars pop up with great frequency.