All the fields I've played at have a 10-20 ft rule that they enforce rather well. That being said, there are some (usually people who play on teams or the die hard weekend warriors) who don't observe that rule.
There are several things I take into account:
1) Age. If they're under 14, no bunkering.
2) Rental. Generally, I won't bunker any rental.
3) Speedball vs. Woodsball. It happens more by accident in Speedball because of the pace. I still hate doing it if it happens and will usually apologize to the player after the game. Woodsball, I've never gotten close enough to bunker. It's rather difficult.
1) Cocky Team players. Sorry to anyone if you are, but I can't stand them. I've been playing for nearly 15 years. I'm a rec player. When I bought my own gear for the first time last January, I bought an Ion. Some of the field team's players who are much younger with "Mommy and Daddy's money" were laughing about my Ion. While my brother-in-law (stock A-5) and I were waiting for other rec players to show up, 3 of these kids challenged us. We played them in 3 vs. 2 and beat them 6 out of 8 times. I mowed a couple down with some extra Heat (literally, I was shooting Diablo Heat
). It felt good because these cocky little bastards thought they were going to walk all over us. I've been playing since they were either A) in diapers or B) non-existent.
2) Die hard Weekend Warriors. Everyone knows these guys. There are usually 4-8 in a group in full camo (not knocking camo because I still wear mine...it's durable as hell). They start talking trash from the moment they pick up their rentals. These guys usually think they are above the rules and start the bunkerfest first. They also have a tendency to wipe and ignore the field boundaries. What they don't understand is that if they want to bunker me, they are taking their 98's at...what...maybe 9/sec against my DM5 or Quest. I may come out bruised, but they're coming out limping.
3) Wipers. All cheaters get something extra, but wipers get even more. I still follow my age rule (a 10 year old doesn't need 15 rounds, but he's get 4 or 5 and a small lecture/warning after the game: "Do that again and you'll get to see how fast I can empty a hopper.").
To recap, I generally hate to bunker period. I don't really care to be bunkered because I don't care how much you play, it still hurts. Even if it is only one or two shots.
It's a "Golden Rule" thing. The whole "Do unto others" thing.