One of the harder parts when it comes to gaming I've found is large combats. In a book, show, movie, or video game large combats are absolutely awesome to see. They're big, dramatic, and action packed. So why doesn't this always convey over to table top? The answer is amazingly simple for most places, and that is that it is hard to feel the action and tension when it is taking upwards of an hour to resolve 6 seconds of action. I went over this a little bit in the Round Timers rant I posted a couple days ago, but I figured a different look into it would also be good. Especially since one of the easiest ways to up the intensity in your combat, is also something that will make everything more dramatic and fun at the same time. That thing isn't a mechanic for the game, but on you specifically as the GM, and it is simply. Keep things moving.
Think about it, even assuming you have 9 players (with you that makes 10 people total), a round taking 60 minutes of game time means that everyone is taking 6 minutes for their turn on average. Why is this? Honestly, it's probably because people aren't using their time well. They're not thinking about what they want to do until you look to them and say "your turn". This doesn't do anyone a service, especially them, as they just add to how long it takes anything to happen and thus increases everyone's boredom. This happening is why a lot of GMs won't run for groups larger than 5, but the problem can happen with those groups as well. Look at your players during combat, how many of them are paying attention to what is going on? How many of them have their heads in the clouds thinking about other stuff, or are talking to another player while they wait for their turn? This isn't doing anyone any favors, let alone the game as a whole. So what can we do about it?
Limit their time to take action
A combat round in most systems is 6 seconds. Now asking someone to give their plan of what they are doing in a round in 6 seconds is a bit drastic, but at the same time so is giving them 5-6 minutes to plan. If I told you to take 6 minutes for each and every NPC you'd think I was crazy, so why is it that you, the GM, who is expected to handle the entire world and all the NPCs is held to a higher standard for decisiveness than a player who only has to worry about their character?
Tell the player that it is their turn, if they have a question or two that is fine, but if they start getting near a minute without telling you what they are doing exactly hold up a hand and slowly pull your fingers in. If you get the whole count down done, state they've taken too long and have thus lost their turn and move on. Keep this up consistently, and they'll get the idea that they don't have all day to plan their action. They'll also start paying attention more when it is not their turn, using those valuable seconds to plan their more complex moves. A minute or two is plenty of time to confirm a few facts, tell the GM what you want to do, and roll the dice.
With just this step alone, our 10 person group has gone from a 50-60 minute round to a 20 minute round of combat by the way, and that is assuming everyone takes the full 2 minutes.
Limit the number of recaps
How much time do you lose explaining the situation to every player during the round? Combat can get confusing, but it shouldn't be so confusing that you have to explain things to every player along the way. Especially not if they're paying attention while other people are acting. So a way to get them paying attention, and saving everyone some time, may be to limit how often you'll recap the situation in a given round. Twice a round for 6 players, three times for 10, or basically 1/3 the amount of players you have seems more than fair.
If the recaps are used for the round, and someone else asks tell them you've already explained it 2-3 times, and you're not doing it again. They'll have to act on unsure knowledge. You do need to be careful with this though, as it favors those with faster initiative for getting these recaps. If someone asks for a recap in close to consecutive rounds, deny them the use of one, and ask them (politely) to pay more attention.
It is important to remember that there is a difference between a full recap and a confirmation. "Is someone pointing a gun at Larry?" is different than "What's going on?" or a player who doesn't even realize that there has been a major change to the battlefield in some way. Answer questions if your players have them, but if they're getting too much into the "What is going on?" scenario, or it is a consistent problem, a polite reminder that they could pay more attention to what is going on might be needed.
If everyone in your group is having trouble keeping up with what is going on however, you may just need to be more clear. Recap the round at the end of it, and give the current situation before topping off the initiative order. If you still have problems, ask your players if you're not being clear and what you can do to fix it. If they say you are being clear, or are just not paying attention when it's not their turn, other steps need to be taken.
Precision is hard
In games where you are using a battle mat, I can't say how many times I've seen combat slowed down as players carefully counted off the squares for their fireball or missile or whatever. Now, in a Dungeon Crawl, or game where the tactical application is important that's fine (but then you wouldn't be worried about combat taking too long now would you?), in a Role Playing scenario though, I've always been simultaneously amazed by how long it can take and why a GM would allow it. That level of precision is incredibly hard to pull off, and most games using mats will point out that characters in melee are often moving back and forth and around each other as they fight. So the question is, if you're looking for smoother flowing combat while upping the intensity, why would you let them carefully count out the squares from their birds eye view?
Instead, have them eye ball it. Have them tell you where it is centered, and give them maybe 5 seconds to choose. More than fair considering the entire thing, along with the confusion of what everyone else is doing, is taking maybe 6 seconds. If it catches an ally, oops. If it misses the enemy, oops. If it works perfectly, well alright then. This should also get them thinking about their action before their turn, and if they use it to count out squares then, well you can't really stop them now can you? However, you both get what you want, you have a player paying attention between their turns, and they get to pin-point where they want their attack to go off. Everyone is winning here.
Pulling It All Together
When you pull it all together, your combat should be running faster and smoother. With luck (or good players), your players will catch on and use their time effectively. Acting quickly in combat, and letting you resolve things faster. Without wasting time on needless recaps, and cutting down on decision making time you also increase the intensity of the scene. Losing an action can be very bad, and if they can't think of one they'll have to act in haste which will make the decision a bit more desperate for them.
Faster flowing combat though feels, well, more like combat. Give players their chance to shine, but don't let them slow things down. After all, what is taking you 20 minutes out of game to resolve is supposed to just be 6 seconds. Those in character six seconds are frantic precisely because people don't have time to fully plan out every little thing they do.
The trick to this is you need to be polite when doing it. Rudeness will cause more issues, and you shouldn't call a player to task on not paying attention in front of everyone else. Talk to them about it privately elsewhere, find out what the problem is. If the problem can be fixed, then do so. If there are differences that can't be fixed and they're unwilling to compromise, maybe its better that they do something else during game time? Especially if they're not having fun.
If they are having fun with every other part of the game, it's a bit trickier. If the game isn't combat focuses, you're in a much better position than if the game is more action oriented. The trick there will be compromise. Even if the compromise is just to minimize their character's role in combat and make up for it elsewhere. Of course, every one and every game's mileage may vary.