Learn Turkish: Rakip şut çekmesin diye ıslık çaldılar. - They whistled so that the opponent wouldn't take a shot.

In Turkish, to express purpose involving a different subject ("so that someone else does or doesn't do something"), you use the 3rd person imperative followed by diye. Çekmesin diye literally translates to "saying 'let him not shoot'," which naturally means "so that he wouldn't shoot."

I'm used to diye meaning "because". How do I know it means "so that" here?

The function of diye shifts depending on the verb form before it. When it follows an imperative or optative verb (like the negative command çekmesin), it indicates purpose ("so that" or "in order to"). When it follows a standard indicative tense (like the past or present), it indicates a reason or assumed reason ("because" or "thinking that").

Could we use the -DI mI (immediate consequence) structure we are learning in this lesson instead of diye?

No, because -DI mI expresses time ("as soon as" or "whenever"). If you said şut çekti mi ıslık çaldılar, it would mean "As soon as he took a shot, they whistled." The original sentence requires expressing a goal or prevention ("so that he wouldn't"), which is exactly what the imperative + diye structure provides.

Why is the verb çekmek (to pull/draw) used for taking a shot?