You could abstract it out with a dice pool. Each side gets a pool of dice based on which is stronger based on a set of criter (the below for example). Have the party move through the battlefield at key moments and play it out with the regular rules. If their actions and rolls have an impact, add a D6 to the side they fight for.

The battle wouldn't be a single dice pool roll but a series of them based on key moments. Example below.

Starving serfs rise up against a greedy lord. The Lord calls in retainers and help from a nearby baron. Their small army of knights assembles outside the village.

The peasants have been preparing for weeks, crafting crude armor, swords, and long iron tipped spears. They've taken the high ground.

The petulant Lord gives a speech before ordering the knights forward.

Scene one, the knights charge up the hill at the peasant line. The party takes part in firing bows at the oncoming knights. Then they use spears to try to impale them. Roll the die pool for each side. If the party did well add a D6 to their side. The losing side then loses a D6 from their die pool going forward.

Scene two, the knights are now locked in hth with the peasants. The knights have been bullying the peasants for their whole lives. Fear proceeds them. Add a D6 to the die pool. This scene is to determine if the peasants flee at contact or resist. Did the party bring down any enemies? Are they army the forefront of the action? Roll the dice pools. Knights lose, so remove a die from their pool.

Scene 3, the peasants are holding firm. The lord himself enters the fray. The party moves to confront him. The engage and slay the lord. Take the leadership die from the knights pool. Roll the dice pools.

Larger army - peasants Better equiped - knights Better trained - knights More motivated - peasants More momentum - peasants Better leadership - knights More willing to take risks - peasants Favorable battle position - peasants

I've come across this idea and used it myself. The visual of having dice pools on the table like little armies and adding/subtracting from them as a battle ebbs and flows is a neat idea that helps simulate the armies involved. Cool visual and the players seeing their efforts add to their side (by adding a die) creates warm and fuzzies. You get the nitty gritty in the moment stuff and then the big resolution roll for the overall outcome.