Learn Arabic (Modern Standard): ما إن هاجم الخصم حتى صد الملاكم الهجوم صدتين. - No sooner had the opponent attacked than the boxer blocked the attack twice.

صدتين is a Cognate Accusative Expressing Quantity. It is derived from the same root as the main verb صد (to block). It is the dual form of the noun of a single instance (صدة, meaning 'one block'). By adding it after the verb, it literally translates to 'blocked... two blocks,' elegantly meaning 'twice.'

Why does the word صدتين end in ـين (-ayn) instead of ـان (-aan)?

As a Cognate Accusative, the word functions as a type of object and must be in the accusative case (mansub). For dual nouns in Arabic, the accusative suffix is ـين (-ayn), which is why we use صدتين rather than the nominative صدتان.

How does the expression ما إن ... حتى work in this sentence?

This is a fixed grammatical structure used to say 'No sooner had... than...' or 'As soon as...'. The phrase ما إن is followed by a past tense verb (هاجم), and حتى introduces the immediate reaction, also usually with a past tense verb (صد). Note that the إن here is just for emphasis and does not act like the conditional 'if,' so it does not alter the following verb.

Could we just use مرتين (two times) instead of صدتين?