Not to defend him, but the tax code is a real mutha for all pro athletes. It's easy for them to get caught up in the BS tax code. Each State, County, City, Country takes a bite out of their earnings. It's a near impossible job to comply.
Think about how many venues a NBA player is in. He has to pay income tax to every State,City etc. he plays in and report his income for everytime he plays there, because they say he earned that income in their local. Add to that games he didn't play in or injuries etc and the huge variations of tax laws in the 50 states and cities.
Screw it up unknowingly a few times and it dosen't get caught for a couple years. Then when it does, the penalties and interest have compounded on themselves and they end up with a multi million dollar price tag.