Brendan Fraleigh, a Certified Financial Planner, breaks down what really happens to a rookie's signing bonus, from taxes and timing to the mistakes that cost players the most.

A client of mine signed his second contract a few years back. Walked into my office looser than I'd ever seen him, cracking jokes, already talking about the watch he wanted. His rookie deal had been the kind of money you're almost afraid to touch. This one felt different. This one felt like arrival. I asked him a simple question before we celebrated anything: what does year four look like, when this contract is over, and the phone isn't ringing? He didn't have an answer. Most

I remember when I first signed. I thought I was invincible. I was 18 with millions of dollars coming my way and a clear path toward...