First, I want to clarify that indeterminism is there exists no fact to the matter about future events. It is different than saying that the future is extremely hard to predict. In other words, some say that a coin flip in indeterministic. However, assuming that all particles (atoms, and molecules, etc) behave in mathematically predictable ways, then an omniscient being, knowing the physical properties of all relevant matter (the coin, air current, force of flip, etc) should be able to predict the outcome. Therefore, a simple coin flip is not evidence of indeterminism, because its out come is theoretically (though not practically) possible to determine. Is this a correct way to interpret the view? Second, where do indeterminist think that indeterminism can come from, given the standard view that all matter follows predictable laws of physics?
I don't work on these things myself, but I'll make one point quickly. Nowadays, it isn't at all obvious that you could predict what will happen when the coin is flipped if you knew all the relevant physical facts about the present, for the simple reason of quantum indeterminacy . It may be that the current physical facts make it overwhelmingly likely, say, that the coin will land heads. But quantum mechanics tells us that it is possible, still, that, when you flip the coin, it will turn into a dove and fly away, let alone that it will land tails. So many people think that physics itself speaks against determinism, not in favor of it. Not everyone, mind you, but plenty of people.