Count Dooku uses his action during his turn to use the Force to hurl a large hunk of something to crush the helpless Obi-Wan and Anakin. He used the Force to do it so it is obvious that he was using his action during the NPC initiative slot that was up in the initiative order.
The next initiative slot is for the PCs and Yoda uses it to activate a Force power and catch the large hunk of something thereby saving his friends. He activates his Force power so it was an Action and it had to be done during the PC initiative slot that fell next in the order.
The only problem with this is that it can’t be done within the RAW of the FFG Star Wars RPG system. By the time that Yoda uses an Action to activate his Force power the attack that Count Dooku has launched will have already happened. You can’t make that claim that the PC group used a destiny point to make Dooku fail in his attack, because if that was the case Yoda would not have activated his Force power and used an Action to do so.
How does one resolve situations like this in a game mechanic that makes no allowance for character reacting, or interrupting, another character action?