So I'm aware Game of Thrones is fantasy, and so isn't completely historically accurate. But I'm also aware that it's also heavily based on medieval history. So I was wondering, what about the latest episode was true to what happened in the past?
Your question was asked in a similar fashion by /u/TJ_Henry_Yoshi, which you can find here. In the linked thread, you'll find /u/Valkine discussing several key elements of the battle and it's accuracy compared to medieval battles.
This leads to some discussion with several users. A notable comment regarding your question can be found here, by /u/Samuel_I, in which he compares the surrounding during the battle of the bastards to the battle of Cannae. Note that this is not a medieval battle.
P.S. GOT spoilers, obviously.