A resolution was taken to retreat, i.e., run away as fast as we could.

From 1776 by David McCulough. Page 288.

Washington’s plan, as at Trenton, was again to divide his force, with Greene’s column going off to the left, Sullivan’s column to the right.

The battle broke out at sunrise, Friday, January 3, when Greene’s vanguard and British forces ran into each other by chance two miles out from Princeton. General Hugh Mercer with several hundred men went off to the left to destroy a bridge on the King’s Highway, to stop any enemy retreat from the town in that direction. Mercer and his men arrived just as the British commander at Princeton, Colonel Charles Mawhood, and two regiments were setting off from Princeton to join Cornwallis at Trenton.

For the British the appearance of the Americans at that hour and in such numbers was totally unexpected. “They could not possibly suppose it was our army, for that, they took for granted, was cooped up near Trenton,” Knox would write. “I believe they were as much astonished as if an army had dropped perpendicularly upon them. However, they had not much time for consideration.”

Both sides opened fire, and in a battle that quickly escalated on the sweeping open fields and orchard of William Clarke’s farm, the fighting turned as furious as any of the war, the dead and bleeding strewn everywhere.

Mercer, who had dismounted when his horse was hit in the midst of a British bayonet attack, fought with his sword until he was clubbed to the ground, then bayoneted repeatedly—bayoneted seven times—and left for dead. Colonel John Haslet, who tried to rally the brigade, was killed instantly by a bullet in the head.

More Americans rushed forward, many of them Pennsylvania militia with little or no training, who refused to yield, as Washington, Greene, and Cadwalader rode among them to lead the way. The sight of Washington set an example of courage such as he had never seen, wrote one young officer afterward. “I shall never forget what I felt…when I saw him brave all the dangers of the field and his important life hanging as it were by a single hair with a thousand deaths flying around him. Believe me, I thought not of myself.”

“Parade with us, my brave fellows,” Washington is said to have called out to them. “There is but a handful of the enemy, and we will have them directly!”

More Americans descended on the enemy’s flanks and Mawhood and his redcoats were soon in full flight toward Trenton. (“A resolution was taken to retreat,” remembered one of Mawhood’s junior officers, “i.e., run away as fast as we could.”) Washington, unable to resist, spurred his horse and took after them, shouting, “It’s a fine fox chase, my boys!”

The ferocious battle on the Clarke farm, the deciding action of the day, had lasted all of fifteen minutes.

By the time Washington had reigned in his horse and called off the pursuit, another part of the army had entered the town, where some 200 of the British garrisoned there had barricaded themselves inside the large stone main building of the college, Nassau Hall. When Captain Alexander Hamilton and his artillerymen fired a few rounds into the building, the redcoats gave up.

The American dead numbered 23, including Colonel Haslet and General Mercer, who suffered nine days before dying of his wounds. Mercer, a doctor and pharmacist in civilian life who came from Fredericksburg, Virginia, not far from Mount Vernon, had been a favorite of Washington’s.

But losses were greater in British dead and wounded, and the Americans had taken three hundred prisoners. The British, though greatly outnumbered, had put up a fierce fight. But for Washington and the army it was another stunning, unexpected victory.”