Can you try out for a college football team?

Most colleges allow "Walk On"(non-scholarship) players and have tryouts to fill those spots. I believe NCAA rules allow Div. I football programs to have up to 20 walk-ons.
Division II schools(half scholarship), usually have a good number of walk-ons on their teams while Division III schools(no scholarships) are basically all walk-ons
You must never have been paid to play at any level of pro football and be a student at the college, of course.