Ithink he could have played better than he (do).

I think he could have played better than he did.

could have + v-ed 表示过去应该能做到什么事，但却没有做到的意思。

could have done 是指本可以做而没有做
原句应为I think he could have played better than he did.
意思是指我觉得他本应该play的更好

这种用过去时的方式表示事与愿违，英语中常用的方法。

虚拟语气。。。
表示已经发生过的事，无法重复
did