Learn Farsi: قهرمان می‌توانست حریف را شکست دهد.

We use the past continuous form of the verb "to be able to", which is mi-tavanest (was able to). Because Farsi links these concepts by saying "was able that he defeats", the second verb must be in the present subjunctive form: shekast dahad.

Why does the subjunctive verb shekast dahad not have the usual be- prefix?

The verb for "to defeat" is shekast dadan, which is a compound verb literally meaning "to give defeat." With many compound verbs in Farsi, the be- prefix for the subjunctive is dropped because the first word already carries the main meaning. Thus, we use shekast dahad instead of shekast bedahad.

How do we get the form dahad from the verb meaning "to give"?

The infinitive is dadan. To make the present subjunctive, we need the present stem, which is irregular: dah-. We then add the 3rd person singular ending -ad (matching "the champion"), which gives us dahad.

Why do we need the word ra after harif (opponent)?

The word ra points out the specific direct object of the sentence. Because the champion is defeating a specific, known person ("the opponent" rather than just "an opponent"), we place ra immediately after harif to show exactly who is receiving the action.