During the late Eastern Han Dynasty, as warlords vied for supremacy, Ma Teng, the governor of Xiliang, was killed by Cao Cao. To avenge his father, Ma Teng's son Ma Chao led hundreds of thousands of Xiliang troops into the Central Plains, breaking through key passes like Tong Pass and Chang'an, and faced off against Cao Cao's main army at the Wei River mouth.
Cao Cao had a fierce general named Xu Chu, known as the Tiger Marquis, whose reputation had long reached Ma Chao. When the two armies faced off, Ma Chao asked, "I hear there is a Tiger Marquis in your camp—is he here?" Xu Chu, standing behind Cao Cao, bellowed, "I am the Tiger Marquis! Do you dare to fight me for a hundred rounds?"
Ma Chao, another fierce general from the Western Liang, charged out with him, and the two engaged in a furious duel. They clashed for over a hundred rounds, neither gaining the upper hand. Their horses, exhausted, were swapped for fresh mounts, and they fought another hundred rounds, still deadlocked.
Xu Chu, caught up in the heat of battle, wheeled his horse back to his own lines, stripped off his armor to reveal his powerful, muscular frame, and then, bare-chested and gripping his blade, mounted his horse once more to resume his duel with Ma Chao. Soldiers on both sides, having never witnessed such a ferocious fight, were utterly stunned.
After dozens more rounds of fierce combat, Xu Chu summoned his divine strength and raised his blade to strike at Ma Chao. Ma Chao sidestepped the blow and thrust his spear toward Xu Chu. Xu Chu cast aside his own weapon, clamped his arms around Ma Chao's spear, and the two wrestled for control.
Xu Zhu, possessing immense strength, snapped the spear shaft with a loud crack, and the two men then fought wildly on horseback, each wielding half a broken spear.
The two armies then clashed in a chaotic battle, with casualties on both sides, before each withdrew. Upon returning to his camp, Ma Chao said to his ally Han Sui, who had come with him:
"Xu Chu's bravery is rare in the world—he truly is a 'Tiger Fool'!" Later, the idiom "fighting bareback" came to describe reckless combat without strategy, or a headlong, all-out assault.
Source: *Romance of the Three Kingdoms*
Meaning of the Idiom: Later, the Chinese idiom "赤膊上阵" came to describe how reckless combat without strategy, or a headlong, all-out assault.