Learn Turkish: Hemşire az kalsın sargıyı yanlış bacağa sarıyordu. - The nurse almost wrapped the bandage on the wrong leg.

This is the core of how Turkish handles averted actions! To say someone almost did something or was on the verge of doing something, you pair az kalsın (or neredeyse) with the past continuous tense (-yordu). Think of it as 'she was in the process of wrapping it, but got stopped.' If you used the simple past (sardı), it would mean she actually completed the action.

Could I use neredeyse instead of az kalsın in this sentence?

Yes, absolutely. Neredeyse and az kalsın are interchangeable for these 'almost happened' scenarios. Az kalsın often carries a slightly stronger sense of 'narrowly escaped' or 'narrowly avoided', making it perfect for a medical mistake like this one, but neredeyse would be just as natural here.

Why does bacak (leg) take the dative case and become bacağa?

The verb sarmak (to wrap) requires the dative case for the destination, meaning the thing you are wrapping something onto or around. Since she is wrapping the bandage onto the wrong leg, yanlış bacak gets the dative ending -a, which also causes the final -k to soften into a -ğ (bacağa).

Why does sargı have the -yı ending?