I'm no CPA or anything close... I hire that our also. I live in one state (Washington) with no income tax and work in another (Oregon) that levies a 10% tax (must be for all the infrastructure I don't use...). I only pay OR taxes for the days I actually work in Oregon. The taxes are pro-rated. If WA had a 5% tax, then I would owe Oregon the larger amount, less what I paid to my own state. I think the same is true for these out of state athletes...Pretty sure Seahawk players owe taxes on 1/16 of their pay when they play a game in Oakland, LA, San Jose or San Diego... whereas Dallas, Miami... not so much, eh? I can see the advantage to getting more of the pay in bonus money, if I was a Seahawk. Other locations will be in between these extremes... However, if you LIVE IN California, there is no escaping it whether on the road or not - unless some other state has a higher tax, then you may owe a bit more somewhere else...
That's how I see it. And really, even less of a big deal for someone with a roomful of accountants...