The warfare in the novel isn't really historically grounded for the time period. There's quite a lot more duels between officers depicted in the novel than there are in the contemporary historical records of the time.
- There's Lu Bu dueling Guo Si (Lu Bu was forced to withdraw once Guo Si's cavalry showed up)
- The action where Guan Yu charged through Yan Liang's troops, impaled him with his spear, cut off his head, and returned to Cao Cao's lines
- Yan Xing wounding and nearly killing Ma Chao (Ma Chao's men showed up and Yan Xing was forced to withdraw)
- Taishi Ci and Sun Ce fighting it out hand to hand, both of their retinues show up, the two withdraw; Taishi Ci takes Bofu's helmet, Sun Ce takes Ziyi's short ji.
Those are the only four that there are actual records for. In addition, the novel makes use of quite a few fantastical style formations (and methods in breaking them), weapons that didn't exist for another 900 years later (the big heavy axes, wolf teeth clubs, crescent halberds, etc), and the utilization of gunpowder signals which didn't exist at the time either. Not only does the novel not give a good depiction of Three Kingdoms era combat, it doesn't even give a good depiction of Song to Ming dynasty combat.