STANFORD, Calif.  As he pedaled through campus on a sunny morning last week, Stanford quarterback Andrew Luck explained the two clear plastic bags covering his bike seat. At a cradle of technological ingenuity, Luck had found a low-tech solution for shielding his posterior from the morning dew.

“Bookstore bags work the best,” he said, shrugging.

The image of Luck biking with his peers instead of driving off to N.F.L. riches is fitting. Yet many who do not know him were surprised that he gave up the opportunity to become the first pick in April’s N.F.L. draft to return to Stanford for his senior year.

Luck passed up guaranteed millions to earn a degree in architectural design from the School of Engineering, avoiding the glare of the N.F.L. spotlight to blend in on this palm-tree-lined campus, once home to people like Herbert Hoover and Tiger Woods.

“He’s someone doing something that conventional wisdom says is not the thing to do,” said David Shaw, a Stanford graduate who was named the Cardinal’s football coach last month. “But the people here say, ‘I understand.’ ”