Upon further review: these states do not distinguish between games of chance and games of skill, thereby making gambling on pool an arrestable offense (although they still have plenty of pool tournaments in these states)
Arizona, Arkansas, Florida, Illinois, Iowa, Louisiana, and Maryland
And these states are still up in the air with their individual laws concerning this, making it questionable in each:
Delaware, Montana, Tennessee, and Vermont.
In all other states it is completely legal to wager on games of skill that are recognized by each state.