At the risk of being called a bunch of names I am going to weigh in on this. I did some research just to make sure I am not talking stupid. Assuming all athletes are employees of a team they are taxed based on their residence. So if I play for Miami but live in California then I pay taxes on the state I live in. Now it is different if I go to a state and actually work there at a job that originates there. That is different than if I live in Florida and go play a game in California. If I lived in Florida and went to Cali and took a job that paid a wage then I would have to file a return there.
Just going across the state lines to work doesn't change anything. You are still working for your employer wherever he sends you but where you live is the key factor. Can you imagine the truck drivers tax returns? Some of them are in multiple states each year.
I have no idea what a COLA (cost of living adjustment) has to do with taxes.
Contract labor is a totally different animal. You are basically self employed at that point and have all sorts of tax obligations and tax advantages. Not sure why you even brought that up.
Players and coaches are paid an agreed to amount and divided by the number of pay periods they have - monthly, weekly, two times a month, etc. Never heard that one game was more valuable than another. They are all the same unless you can show some weird example out there besides just an opinion.
Not sure what the SIT deduction is. You would have to explain that one to me, googled it.
Please tell me who your tax adviser is so I do not use them.
You are totally wrong. I have a CPA license and research via legal software not google searches. Players and coaches apportion taxes to states via "Duty Days" but people know it as "Jock Taxes" . If you want a license to research this information, CCH.com is pretty good. But below are a couple of articles about it. (these articles are not authoritative, only regs, court rulings, and the states tax code, etc. are authoritative really. However, you need a subscription for the most part for that stuff. so I can't link).
http://articles.latimes.com/2009/apr/12/sports/sp-jock-tax12
http://www.pressherald.com/2015/06/28/pro-athletes-pay-a-big-price-for-their-success-in-taxes/
SIT deduction is "State income tax" deduction. Pretty much the most basic itemized deduction there is. Who does your taxes?
COLA had to do with the economic wealth, not taxes. As I stated. Reread my original post you idiot where i state "economically" and not "tax wise" and econmically it makes a lot of difference. Sorry you can't keep up.
Also note every state is different the way they tax. Some home states tax everything and give a tax credit to taxes paid to other states. Some states, such as South Carolina only tax their own income generally. Below is a helpful website.
http://www.mtc.gov/The-Commission/Multistate-Tax-Compact
Generally speaking, de minims law set in for Service workers. So the only workers that usually have to end up apportioning income is those that have wages that go directly into the product such as contractors. (note didn't say independent contractors, contractors can have payroll) . But even that is not always. It varies from state to state, etc. Nexus laws are always the first place to look.
But back to the main topic, Athletes are taxed by each state they play in (if that state has a state income tax). So are coaches. Again, it's based off of duty days. I don't know how many duty days they are given or how that math works. I don't work for a MLB team, etc. But I am pretty sure if you have 4 road games, I doubt only 4 of 365 days is taxed to those states. It's much higher. 1 duty day doesn't necessarily = 1 work day. It doesn't in baseball. That you can find on your own. Also, college coaches probably have to factor in recruiting trips too. But again not sure.
But I do know any geek on the street that has taken a tax law class knows about duty days and how athletes & coaches having to apportion income to multiple states. The case was a landmark case and one that most professors try to teach in class since its some what interesting. Also, read stories about why Vernon Wells found it more profitable to be cut then to play.
Whatever your job is, don't quit it. You wouldn't make a good CPA or financial planner. Google searches don't work in those fields. You have to have better research tools and the thing about law and tax, you hardly ever come away with home runs. Theres always questions. Nothing is ever cut an dry. The fact that you tried to do google searches on this and now you think you have it makes me think your probably a narcissist.