Picture a game where the rules are on the wall and everyone can see them. Both sides play to those rules, and neither side goes looking for an advantage that is not written there. What matters in that picture is not the score — it is that the same rules covered both sides the whole way through. Everything this word does grows from that: honest dealing away from the field, and even a short spoken line that hands someone their due.
From the picture
口語：給人一個公道的肯定
從「照規矩評斷」再走一步，就成了對「人」的一句評語：把公道那把尺拿出來量一量，結論是這個人做得對，於是講出口。這個意思只活在 fair play to somebody 這個固定說法裡，光是 fair play 兩個字並不帶這個用法。
noun · C2
Said when you think someone was right to do what they did, or that they deserve some credit for it. Spoken, and used mostly in British and Irish English.
算他做得對
noun · C2
Playing a game by its rules, without cheating and without taking an advantage that the rules do not allow.
公平競賽
noun · C2
Honest, even-handed treatment of people, where nobody cheats, lies, or is quietly given an advantage over the others.
公道