Learn Swedish: Vardera laget spelade mycket offensiv fotboll. - Each team played very offensive football.

Unlike varje (each/every), which requires an indefinite noun (like varje lag), the formal dual determiners vardera, ingendera, and endera take the definite form of the noun. This is why it is vardera laget.

Why use vardera here instead of varje?

Vardera specifically means "each of two". Since a football match always involves exactly two teams, vardera is the most precise choice. If you were talking about "each team" in a large tournament with many teams, you would use varje lag.

Since lag is an ett-word, shouldn't it be vartdera laget?

Strictly speaking, the neuter form is indeed vartdera. However, in modern Swedish, the en-word form vardera has become widely accepted and is very commonly used for both genders. You will encounter both vardera laget and vartdera laget.

Why is the adjective offensiv not in the neuter form offensivt, considering the teams are playing a game (ett spel)?