Learn Russian: Папа смотрел телевизор, когда я звонил.

Папа смотрел телевизор, когда я звонил.

Dad was watching TV when I called.

Breakdown of Папа смотрел телевизор, когда я звонил.

to watch / to look at / make sure (in a warning)

Questions & Answers about Папа смотрел телевизор, когда я звонил.

Why does the sentence use звонил (imperfective) instead of позвонил (perfective) for "called"?

The imperfective звонил focuses on the process or the general fact of the action, closer to "I was making a call" or "during my call." If you wanted to emphasize the exact completed moment the call connected (interrupting his TV watching), you would use the perfective позвонил.

Why doesn't the word телевизор change its ending if it is the direct object?

You are right that direct objects take the accusative case. However, for masculine nouns that are inanimate (objects, not living things), the accusative form is exactly the same as the dictionary form. Therefore, телевизор stays exactly the same.

How do we know the person speaking is a man?

In the past tense, Russian verbs must match the gender of the subject. Since я (I) is the one calling, the verb звонил takes the masculine -л ending. A female speaker would say я звонила.

Is the comma before когда strictly required?

Yes! Unlike English, where commas before "when" are often optional, Russian grammar always requires a comma before conjunctions like когда (when), что (that), and потому что (because) when they introduce a new part of the sentence.