If you play 3 years of college basketball how many years can you play college football?

Answer 1

One.

Student athletes are given five years to use four years of eligibility to play sports. It does not start over when a student switches sports.

Of course there is an exception to this rule (as there seems to be with most rules) and that is if the student was medically red-shirted.

Answer 2

I know Nate Robinson played football and Basketball for University of Washington, a major D1 school, so you must be able to. It surely must be difficult since College Football ends around December for most teams and basketball starts at the beginning of November, so how he did it I don't know. But he did.