Legal, yes. Risky? A year ago, people would have laughed at that word. Still now, most don't think so. Personally? I think there's about a 10% chance that the city won't get those dollars back. Further, you should take a look at the federal funds rate and infer what you can from it. I'll leave that to you.
More importantly, though, at this juncture it is arrogant and despicable that an organization would build such an monstrosity when, really, they didn't need to, then overspend by millions to acquire what some see as risky acquisitions only to ask for cash to finance 20% of the entire project.
Normal? Again- a year ago? Most would say sure, the really saavy would say don't. As of two months ago? This idea is close to unbelievable.
This is why when someone like the Florida GM speaks up (albeit somewhat improperly) about the manner in which the Yankees are spending, it holds enough water to be taken seriously.
Perhaps instead of trying to explain how the Yankees are attaining this money, you should start questioning the importance of the state of New York having 200M more in their budget for transportation, schools, and hospitals, particularly when the United States is going through the largest capital crisis incurred since the 70's (and in my opinion not even close to rock bottom).
Cities and states are slashing funding across the board. They are doing this because of a capital shortfall - of which I hope you are well aware. These bonds you speak of are the backbone of developments that provide our basic necessities. If I lived in New York I would be livid about this. It pisses me off to see this living hundreds of miles away, understanding the effect on a macro level. Knowing that the majority on the bonds funding this stadium are actually financed by national taxpayers is even worse. If you don't get it then I'm sorry for you, but trust me- I understand exactly what this means.