Questions & Answers about Я кидаю мяч другу.
Другу is the dative case form of друг (friend).
In Russian, when you say throw something *to someone, the person who receives the object is in the *dative case, not in the basic (nominative) form.
- Nominative (dictionary form): друг – friend
- Dative: другу – to (a) friend
So:
- Я кидаю мяч другу. – I throw the ball to (a) friend.
(другу = to a friend)