I agree with getting him where it hurts...find out what he likes and then use that as leverage.

Also, reiterate the expectations of play several times throughout your day. Tell him - we are going to play gently and I do not want to see you throw toys. Make sure he is looking at you and you have a stern face.

As soon as he misbehaves....stern face and down to his level so he can look at you and you tell him again "We don't throw toys. That empty bucket is not for throwing. I don't like when you do that. Can you stop throwing the toys?" Don't let him go back to play until you have eye contact and he sees that you mean it.

Also...give lots of positive reinforcement to the other kids who are playing properly. Then he may see that positive attention and hugs are better than stern lectures.

And if you see the other kids be silly because the child started acting silly then make eye contact with the others the same way and look serious and say "That is not funny. We play with toys nicely and we cannot throw toys."

THen....if the behaviour continues...start taking away the toys that are being thrown and the buckets he empties or dumps. Make sure that the children see you take it away and explain why. Say that they or he can have it back when they stop throwing