Flanking is not so much cut and dry when it comes to when to do it, or even when it's punishable or not. Until it is I can only offer my opinion and advice.

As it was mentioned here previously, leaving the cover of your teammates adds a significant risk. That risk has to be weighed against the possible benefits. Since the obvious goal of a flank is to catch the other team unaware, the question to answer is, can that be done effectively? Some things to help make that decision involve:

Do you know where all/most of the remaining OpFor are positioned? If you don't then it might be you taken unaware, instead of the targets you are trying to out-position.

Do you create a hole to the objective for the other team by flanking? This is a tough one. Depends on the map - the avenues the OpFor has to the objective. By you displacing to go around and get them in a flank, you may be making it easier for them to reach the objective. This also depends on if your team is still able to effectively cover those avenues and the objective with the displacement of one or even more flankers. This takes a good deal of map knowledge, teamwork, communication, and intel regarding where the opfor is and what the team together thinks they intend to do. Which is why flanking shouldn't be an easy decision or happen often.

Another question is of timing. I see a lot of "flank" maneuvers done at or close to round start. Beyond kill hunting, it's usually pretty clear that the defending team can't come close to answering the previous questions to validate a well thought out flank and at least to me, just looks like they are running off into the unknown to stir up the hornets nest and hopefully get some suicide kills in.

Then there is the "how many" question. How many of us and how many of them? If you are outnumbered, sending out flankers generally means you are creating holes. If you outnumber them, then it's generally more in your favor and your team can hopefully still effectively secure the objective with the loss of flankers. But here's an even trickier wrench in the works: If you outnumber them, they will usually be looking to try to even things up, i.e., pick people off, before moving in. So if they are skirting the map looking for stragglers and targets, do you think that increases your chance of catching them unaware or just helping them achieve their short term goal of picking off your team?

And of course, stealth is important. If you cannot be stealthy and/or don't have the time and patience and good intel which directs where you are going to slowly stealth to, don't even bother.

These are some of the reasons why it is hard to pin down not only when flanking is allowed, but good tactics. Several things should be merging: Teamwork, communication, timing, stealth, objectives not being compromised or holes created, knowing the map, enemy positions, and even enemy intent. Without most of those you might, at best, be doing a deathmatch style flank. With communication, you might be bordering on a teamwork style flank. But with a good mix of all, you are doing a teamwork objective oriented tactical flank.

Who said it was going to be easy?

PS: This is strictly about flanking, coming up around or behind. Playing it forward is something different. Which is also fun. See http://www.tacticalgamer.com/counter...d-defense.html about that.