Love this blog, realistic fighting is one thing you can’t get a feel for from research. Do you have any recommendations for things to keep in mind when two people are fighting as a team against several bad guys? Assuming the two train together and fight together fairly often.
The tactics will change substantially between characters and situation depending on whether or not they’re carrying guns or were trained in a military context. I say military over police or FBI because the military training is all about protecting, defending, and attacking as a unit, not as an individual. Since yours are probably not and I’m guessing you mean hand to hand, I’ll give my advice from that outlook.
Assuming your two characters view each other as evenly matched (and one won’t try to take the brunt of the opposing force on their own), they’re more likely to know each others weaknesses and trust in each others strengths. There will be a level of trust there that will for the most part ensure that they won’t get in each others way.
And while fighting back to back sounds good in theory (it looks great in a movie!) but in a group, it’s terrible. Because of the amount of pushing and jostling that goes on and because standing still is an unbelievably bad idea (unless you’re an Aikido or Tai Chi practioner), they’re more likely to split a group of enemies up evenly by pulling them off in different directions and fighting alone. This way, they’ll be free to drag their own opponents into each other without having to worry about screwing over their partner by accident (and accidents always happen). Remember, in hand to hand, a character can only really reliably fight one opponent at a time, so when fighting against groups, it’s a lot of bouncing around trying to get their opponents to hit each other instead of them, so they can conserve energy.
It also gives you the opportunity to build in narrative tension if there’s an uneven number of opponents, if the opponents in one fight are more coordinated than usual and refuse to be baited from going after their primary target, and things start going south. Remember, bad guys, even one-off ones are people too and some of them also have a history of fighting together. You can get a lot with just a little work on random mook motivation.
As with anything, the more opponents there are, the greater the chance for failure. To stay realistic, try to keep it between four or six (two and three per fighter). Finally, it’s important to keep in mind in fights that things always go wrong or in an unexpected direction on some level for both parties. The personalities of your characters and their own fighting outlook will affect the fight just as much as their technique. A good fighter doesn’t play around with their opponent, but a lot do anyway.