After playing the game that happened before his home, the relationship with this time will be clear. After being transformed into an independent structure, there is a gap between the perfect tense and the past tense because there is no when, and the main clause and the independent component only express the time relationship through the formal differences of their respective verb tenses. Why isn't the past perfect tense followed by the original sentence when? The problem lies in when, when = the particularity at that time, which is a point in time and does not have the continuous process required to complete, so the perfect tense is not needed. After it is transformed into an independent structure, the restriction caused by the particularity of when's time state is lifted, and "completion" naturally becomes a persistent fait accompli, gaining the freedom and strength to express in the perfect tense.