because the reward if he is a good starter is huge, and the risk is rather minimal. Even if Chapman is not good, how much worse can he be than Leake? Broxton last year blew what, 1 more game the entire year than Chapman with similar save/hold opportunities.
So this is not as big of a risk as you guys are making it out to be, and could be a massive reward. Give him half a year to start. If he doesn't work out, no big loss. Send him back to the bullpen and call up Leake (who has plenty of options). Heck, maybe Leake develops more in AAA with less pressure. He has not really had an opportunity to do that.