<p>Here are some examples of schools where, I think, you can’t defer admission after acceptance.<br>
USC (U Southern California)
Hampden-Sydney
Ohio State
Rutgers
Julliard and, I think, most conservatories</p>
<p>Most schools will let you defer admission for a year after acceptance.</p>
<p>I know a kid who took a gap year even though Oberlin refused to allow him that extra year. He had to reapply to colleges, but is happy he took the break.</p>