The way it works is you first throw too many enemies at your PCs. A bit more than they can likely handle. This is okay, because their foes will not be piling up on them. Decide how many foes you would like to attack them at any given time and then keep things moving. Run that many past the group and attack with them each round. This makes sense with pack hunters like wolves and also with mobs of humanoids, especially if they're mounted. The terrain can change how this looks quite a bit. In open areas a wolf pack tactic of surrounding the PC group and attacks from the sides or wherever they're not looking at the moment make sense. Mounted knights charging on a road are probably going to stay on it and charge back and forth.
The idea transcends systems. I've used it in 2nd edition D&D, Earthdawn, and basic set D&D. I'm sure I could use it in other systems as well as long as there aren't map complications.
Example fight:
In a 2nd edition D&D game I had a paladin, fighter, ranger, and crusader (all second level) against a fop (non-combatant enemy leader) and his dozen mounted knights wielding ranseurs (all one hit die). They met on a road and the PCs started combat by getting two rounds to fire ranged weapons at them before they'd be in melee range, but would need one round to swap weapons if they did so. They did a bit of damage and then half the knights were attacking back. All the PCs ended up being attacked at first but as they whittled away at the enemy and described a loose wedge formation, the attacks were concentrated on the most heavily armored PC with some slipping past to attack other front-liners. Every round, which of the two groups of foes was attacking would switch. Towards the middle, an enemy rogue (fifth level but fighting alone at the rear with no backup against armored PCs) took advantage of the situation to try to sneak in. He failed and was noticed, but kept the party busy in the rear as well. For story reasons, the PCs hated the fop and killed him with arrows. Once this happened the remaining knights fought to the death, also for story reasons.
The end result knocked two PCs unconscious, one of whom was revived in battle. The enemy rogue surrendered. And the players felt like they'd just won an epic battle. If I'd played it differently where all the foes could have attacked from the start, I probably would have slaughtered most of the group. Dividing it up let them live through it. Keeping the enemies in motion made it more interesting for the players to visualize. Ranks of foes just twiddling their thumbs and waiting for their comrades to die so they can stab at the PCs always felt off to me.
Hopefully someone finds this idea useful for their games.
My players hate "wave attacks", which I use for intelligent and/or devious enemies. Why expose all your troops to the PC wizard's fireball when you can send them in 5 at a time from different directions? While they focus on the attack from the north, two more enemies pop up from the east and west. Like velociraptors. 
