This is the 11682nd most frequent Russian word.
забастовок
Strikes.
The word "забастовок" (strikes) is used in the genitive case plural here as part of the phrase "серии забастовок" (series of strikes), denoting that strikes are part of the series.
Рабочие участвовали в серии забастовок из-за условий труда.
The workers participated in a series of strikes due to working conditions.
Here, "забастовок" is the genitive case plural of "забастовка" (strike), expressing the reason 'of the strikes', showing its causative role to the sentence's context.
Из-за забастовок городская инфраструктура временно остановилась.
Due to the strikes, the city's infrastructure temporarily came to a halt.
The term "забастовок" appears in the genitive case plural in the expression "избегать новых забастовок" (to avoid new strikes), as it follows the verb "избегать" (to avoid), which requires this case.