(1) Playing college basketball on scholarship is a very different legal status than employment; the scholarship player has to act in accordance with the rules - reasonable rules - that are imposed by the school.
(2) The Home Depot guy in Colorado? His claim would almost certainly be toast. I know of no legal protection based on recreational drug protections.* He almost certainly would be an employee at will, which means that his employment could be terminated for any reason, or no reason at all, except those that are explicitly prohibited by applicable law, which typically means only those classifications that are protected by federal or state statute, or by a local ordinance.
*We could go over to the Cooler and ask CoH, who is a long-time attorney in Colorado. He's never mentioned any protections for employees who smoke pot on their own time . . . .