Learn Turkish: Onlar hücum yaptı mı biz hemen savunmaya geçeriz. - As soon as they attack, we immediately transition to defense.

This is the converb of immediate consequence you are learning in this lesson. When you follow a definite past tense verb (yaptı) with the question particle (mı), it creates a time clause meaning 'as soon as' or 'the moment that' the action happens. It is not a question here.

Why is the first verb in the past tense (yaptı) when the sentence is about a general rule ('we transition')?

That is a fixed rule for this structure. The trigger action in the 'as soon as' clause always takes the definite past tense (-DI), regardless of when it actually happens. The main verb at the end of the sentence (here, the aorist geçeriz) dictates the tense for the whole thought—in this case, a general habit.

Does adding hemen change the meaning, since the -DI mı structure already implies 'as soon as'?

While -DI mı already means 'as soon as,' adding hemen (immediately) in the second clause is very common in Turkish. It acts as an intensifier, emphasizing just how instantaneous our reaction is when they attack.

Why do we use the verb geçmek (geçeriz) here for 'transition'?

The verb geçmek literally means 'to pass,' but it is the standard way to express shifting into a new state, mode, or phase. The phrase savunmaya geçmek is a very common set expression meaning 'to go on the defensive' or 'to switch to defense.'