Learn Swedish: Taktiken var mer offensiv under förlängningen. - The tactic was more offensive during the extra time.

While many Swedish adjectives take the suffix -are in the comparative, longer adjectives (usually three syllables or more) and many loan words use mer (more) instead. Because offensiv is a longer loan word, mer offensiv is the standard way to form the comparative.

How does the word förlängningen translate to "the extra time"?

The base word is en förlängning, which literally means "an extension" (from the verb att förlänga, to extend). In a sports context, this is the standard Swedish term for "overtime" or "extra time".

Why use under here to mean "during"?

In Swedish, the preposition under means both "under" (physical location) and "during" (time). When followed by an event or a period of time like förlängningen, it is the direct equivalent of "during".

Could I say Taktiken var offensivare anyway, or is it completely wrong?

It is not grammatically forbidden, and you might occasionally hear native speakers use offensivare. However, for adjectives ending in -iv (like effektiv, aggressiv, or offensiv), using mer sounds much more natural and is the recommended practice.