So instead of the car rental/hotel tax going to public goods like new roads, better water treatment facilities, etc., it goes towards a new stadium so the local tax payers are paying more for infrastructure than they otherwise would be. That still sounds like a subsidy to me.
CN is right. The government shouldn't be involved, at all and at any level, with professional sports. It's a completely nonessential good the free market can effectively manage (and I'm by no stretch of the imagination a big believer in free market self regulation).
I also have a hard time believing cities like Baltimore and Cleveland (two cities with the most heavy stadium subsidies) are generating that much in tourism revenue. How many people do you know have ever taken a vacation to Baltimore?